# SQLAlchemy 2.0 Documentation

# SQLAlchemy 2.0 Documentation

# 0.5 Changelog

## 0.5.9

no release date

### sql

- Fixed erroneous self_group() call in expression package.
  References: [#1661](https://www.sqlalchemy.org/trac/ticket/1661)

## 0.5.8

Released: Sat Jan 16 2010

### sql

- The copy() method on Column now supports uninitialized,
  unnamed Column objects. This allows easy creation of
  declarative helpers which place common columns on multiple
  subclasses.
- Default generators like Sequence() translate correctly
  across a copy() operation.
- Sequence() and other DefaultGenerator objects are accepted
  as the value for the “default” and “onupdate” keyword
  arguments of Column, in addition to being accepted
  positionally.
- Fixed a column arithmetic bug that affected column
  correspondence for cloned selectables which contain
  free-standing column expressions.   This bug is
  generally only noticeable when exercising newer
  ORM behavior only available in 0.6 via,
  but is more correct at the SQL expression level
  as well.
  References: [#1568](https://www.sqlalchemy.org/trac/ticket/1568), [#1617](https://www.sqlalchemy.org/trac/ticket/1617)

### postgresql

- The extract() function, which was slightly improved in
  0.5.7, needed a lot more work to generate the correct
  typecast (the typecasts appear to be necessary in PG’s
  EXTRACT quite a lot of the time).  The typecast is
  now generated using a rule dictionary based
  on PG’s documentation for date/time/interval arithmetic.
  It also accepts text() constructs again, which was broken
  in 0.5.7.
  References: [#1647](https://www.sqlalchemy.org/trac/ticket/1647)

### misc

- Recognize more errors as disconnections.
  References: [#1646](https://www.sqlalchemy.org/trac/ticket/1646)

## 0.5.7

Released: Sat Dec 26 2009

### orm

- contains_eager() now works with the automatically
  generated subquery that results when you say
  “query(Parent).join(Parent.somejoinedsubclass)”, i.e.
  when Parent joins to a joined-table-inheritance subclass.
  Previously contains_eager() would erroneously add the
  subclass table to the query separately producing a
  cartesian product.  An example is in the ticket
  description.
  References: [#1543](https://www.sqlalchemy.org/trac/ticket/1543)
- query.options() now only propagate to loaded objects
  for potential further sub-loads only for options where
  such behavior is relevant, keeping
  various unserializable options like those generated
  by contains_eager() out of individual instance states.
  References: [#1553](https://www.sqlalchemy.org/trac/ticket/1553)
- Session.execute() now locates table- and
  mapper-specific binds based on a passed
  in expression which is an insert()/update()/delete()
  construct.
  References: [#1054](https://www.sqlalchemy.org/trac/ticket/1054)
- Session.merge() now properly overwrites a many-to-one or
  uselist=False attribute to None if the attribute
  is also None in the given object to be merged.
- Fixed a needless select which would occur when merging
  transient objects that contained a null primary key
  identifier.
  References: [#1618](https://www.sqlalchemy.org/trac/ticket/1618)
- Mutable collection passed to the “extension” attribute
  of relation(), column_property() etc. will not be mutated
  or shared among multiple instrumentation calls, preventing
  duplicate extensions, such as backref populators,
  from being inserted into the list.
  References: [#1585](https://www.sqlalchemy.org/trac/ticket/1585)
- Fixed the call to get_committed_value() on CompositeProperty.
  References: [#1504](https://www.sqlalchemy.org/trac/ticket/1504)
- Fixed bug where Query would crash if a join() with no clear
  “left” side were called when a non-mapped column entity
  appeared in the columns list.
  References: [#1602](https://www.sqlalchemy.org/trac/ticket/1602)
- Fixed bug whereby composite columns wouldn’t load properly
  when configured on a joined-table subclass, introduced in
  version 0.5.6 as a result of the fix for. thx to Scott Torborg.
  References: [#1480](https://www.sqlalchemy.org/trac/ticket/1480), [#1616](https://www.sqlalchemy.org/trac/ticket/1616)
- The “use get” behavior of many-to-one relations, i.e. that a
  lazy load will fallback to the possibly cached query.get()
  value, now works across join conditions where the two compared
  types are not exactly the same class, but share the same
  “affinity” - i.e. Integer and SmallInteger.  Also allows
  combinations of reflected and non-reflected types to work
  with 0.5 style type reflection, such as PGText/Text (note 0.6
  reflects types as their generic versions).
  References: [#1556](https://www.sqlalchemy.org/trac/ticket/1556)
- Fixed bug in query.update() when passing Cls.attribute
  as keys in the value dict and using synchronize_session=’expire’
  (‘fetch’ in 0.6).
  References: [#1436](https://www.sqlalchemy.org/trac/ticket/1436)

### sql

- Fixed bug in two-phase transaction whereby commit() method
  didn’t set the full state which allows subsequent close()
  call to succeed.
  References: [#1603](https://www.sqlalchemy.org/trac/ticket/1603)
- Fixed the “numeric” paramstyle, which apparently is the
  default paramstyle used by Informixdb.
- Repeat expressions in the columns clause of a select
  are deduped based on the identity of each clause element,
  not the actual string.  This allows positional
  elements to render correctly even if they all render
  identically, such as “qmark” style bind parameters.
  References: [#1574](https://www.sqlalchemy.org/trac/ticket/1574)
- The cursor associated with connection pool connections
  (i.e. _CursorFairy) now proxies __iter__() to the
  underlying cursor correctly.
  References: [#1632](https://www.sqlalchemy.org/trac/ticket/1632)
- types now support an “affinity comparison” operation, i.e.
  that an Integer/SmallInteger are “compatible”, or
  a Text/String, PickleType/Binary, etc.  Part of.
  References: [#1556](https://www.sqlalchemy.org/trac/ticket/1556)
- Fixed bug preventing alias() of an alias() from being
  cloned or adapted (occurs frequently in ORM operations).
  References: [#1641](https://www.sqlalchemy.org/trac/ticket/1641)

### postgresql

- Added support for reflecting the DOUBLE PRECISION type,
  via a new postgres.PGDoublePrecision object.
  This is postgresql.DOUBLE_PRECISION in 0.6.
  References: [#1085](https://www.sqlalchemy.org/trac/ticket/1085)
- Added support for reflecting the INTERVAL YEAR TO MONTH
  and INTERVAL DAY TO SECOND syntaxes of the INTERVAL
  type.
  References: [#460](https://www.sqlalchemy.org/trac/ticket/460)
- Corrected the “has_sequence” query to take current schema,
  or explicit sequence-stated schema, into account.
  References: [#1576](https://www.sqlalchemy.org/trac/ticket/1576)
- Fixed the behavior of extract() to apply operator
  precedence rules to the “::” operator when applying
  the “timestamp” cast - ensures proper parenthesization.
  References: [#1611](https://www.sqlalchemy.org/trac/ticket/1611)

### sqlite

- sqlite dialect properly generates CREATE INDEX for a table
  that is in an alternate schema.
  References: [#1439](https://www.sqlalchemy.org/trac/ticket/1439)

### mssql

- Changed the name of TrustedConnection to
  Trusted_Connection when constructing pyodbc connect
  arguments
  References: [#1561](https://www.sqlalchemy.org/trac/ticket/1561)

### oracle

- The “table_names” dialect function, used by MetaData
  .reflect(), omits “index overflow tables”, a system
  table generated by Oracle when “index only tables”
  with overflow are used.  These tables aren’t accessible
  via SQL and can’t be reflected.
  References: [#1637](https://www.sqlalchemy.org/trac/ticket/1637)

### misc

- A column can be added to a joined-table declarative
  superclass after the class has been constructed
  (i.e. via class-level attribute assignment), and
  the column will be propagated down to
  subclasses.  This is the reverse
  situation as that of, fixed in 0.5.6.
  References: [#1523](https://www.sqlalchemy.org/trac/ticket/1523), [#1570](https://www.sqlalchemy.org/trac/ticket/1570)
- Fixed a slight inaccuracy in the sharding example.
  Comparing equivalence of columns in the ORM is best
  accomplished using col1.shares_lineage(col2).
  References: [#1491](https://www.sqlalchemy.org/trac/ticket/1491)
- Removed unused load() method from ShardedQuery.
  References: [#1606](https://www.sqlalchemy.org/trac/ticket/1606)

## 0.5.6

Released: Sat Sep 12 2009

### orm

- Fixed bug whereby inheritance discriminator part of a
  composite primary key would fail on updates.
  Continuation of.
  References: [#1300](https://www.sqlalchemy.org/trac/ticket/1300)
- Fixed bug which disallowed one side of a many-to-many
  bidirectional reference to declare itself as “viewonly”
  References: [#1507](https://www.sqlalchemy.org/trac/ticket/1507)
- Added an assertion that prevents a @validates function
  or other AttributeExtension from loading an unloaded
  collection such that internal state may be corrupted.
  References: [#1526](https://www.sqlalchemy.org/trac/ticket/1526)
- Fixed bug which prevented two entities from mutually
  replacing each other’s primary key values within a single
  flush() for some orderings of operations.
  References: [#1519](https://www.sqlalchemy.org/trac/ticket/1519)
- Fixed an obscure issue whereby a joined-table subclass
  with a self-referential eager load on the base class
  would populate the related object’s “subclass” table with
  data from the “subclass” table of the parent.
  References: [#1485](https://www.sqlalchemy.org/trac/ticket/1485)
- relations() now have greater ability to be “overridden”,
  meaning a subclass that explicitly specifies a relation()
  overriding that of the parent class will be honored
  during a flush.  This is currently to support
  many-to-many relations from concrete inheritance setups.
  Outside of that use case, YMMV.
  References: [#1477](https://www.sqlalchemy.org/trac/ticket/1477)
- Squeezed a few more unnecessary “lazy loads” out of
  relation().  When a collection is mutated, many-to-one
  backrefs on the other side will not fire off to load
  the “old” value, unless “single_parent=True” is set.
  A direct assignment of a many-to-one still loads
  the “old” value in order to update backref collections
  on that value, which may be present in the session
  already, thus maintaining the 0.5 behavioral contract.
  References: [#1483](https://www.sqlalchemy.org/trac/ticket/1483)
- Fixed bug whereby a load/refresh of joined table
  inheritance attributes which were based on
  column_property() or similar would fail to evaluate.
  References: [#1480](https://www.sqlalchemy.org/trac/ticket/1480)
- Improved support for MapperProperty objects overriding
  that of an inherited mapper for non-concrete
  inheritance setups - attribute extensions won’t randomly
  collide with each other.
  References: [#1488](https://www.sqlalchemy.org/trac/ticket/1488)
- UPDATE and DELETE do not support ORDER BY, LIMIT, OFFSET,
  etc. in standard SQL.  Query.update() and Query.delete()
  now raise an exception if any of limit(), offset(),
  order_by(), group_by(), or distinct() have been
  called.
  References: [#1487](https://www.sqlalchemy.org/trac/ticket/1487)
- Added AttributeExtension to sqlalchemy.orm.__all__
- Improved error message when query() is called with
  a non-SQL /entity expression.
  References: [#1476](https://www.sqlalchemy.org/trac/ticket/1476)
- Using False or 0 as a polymorphic discriminator now
  works on the base class as well as a subclass.
  References: [#1440](https://www.sqlalchemy.org/trac/ticket/1440)
- Added enable_assertions(False) to Query which disables
  the usual assertions for expected state - used
  by Query subclasses to engineer custom state..  See
  [https://www.sqlalchemy.org/trac/wiki/UsageRecipes/PreFilteredQuery](https://www.sqlalchemy.org/trac/wiki/UsageRecipes/PreFilteredQuery)
  for an example.
  References: [#1424](https://www.sqlalchemy.org/trac/ticket/1424)
- Fixed recursion issue which occurred if a mapped object’s
  __len__() or __nonzero__() method resulted in state
  changes.
  References: [#1501](https://www.sqlalchemy.org/trac/ticket/1501)
- Fixed incorrect exception raise in
  Weak/StrongIdentityMap.add()
  References: [#1506](https://www.sqlalchemy.org/trac/ticket/1506)
- Fixed the error message for “could not find a FROM clause”
  in query.join() which would fail to issue correctly
  if the query was against a pure SQL construct.
  References: [#1522](https://www.sqlalchemy.org/trac/ticket/1522)
- Fixed a somewhat hypothetical issue which would result
  in the wrong primary key being calculated for a mapper
  using the old polymorphic_union function - but this
  is old stuff.
  References: [#1486](https://www.sqlalchemy.org/trac/ticket/1486)

### sql

- Fixed column.copy() to copy defaults and onupdates.
  References: [#1373](https://www.sqlalchemy.org/trac/ticket/1373)
- Fixed a bug in extract() introduced in 0.5.4 whereby
  the string “field” argument was getting treated as a
  ClauseElement, causing various errors within more
  complex SQL transformations.
- Unary expressions such as DISTINCT propagate their
  type handling to result sets, allowing conversions like
  unicode and such to take place.
  References: [#1420](https://www.sqlalchemy.org/trac/ticket/1420)
- Fixed bug in Table and Column whereby passing empty
  dict for “info” argument would raise an exception.
  References: [#1482](https://www.sqlalchemy.org/trac/ticket/1482)

### oracle

- Backported 0.6 fix for Oracle alias names not getting
  truncated.
  References: [#1309](https://www.sqlalchemy.org/trac/ticket/1309)

### misc

- The collection proxies produced by associationproxy are now
  pickleable.  A user-defined proxy_factory however
  is still not pickleable unless it defines __getstate__
  and __setstate__.
  References: [#1446](https://www.sqlalchemy.org/trac/ticket/1446)
- Declarative will raise an informative exception if
  __table_args__ is passed as a tuple with no dict argument.
  Improved documentation.
  References: [#1468](https://www.sqlalchemy.org/trac/ticket/1468)
- Table objects declared in the MetaData can now be used
  in string expressions sent to primaryjoin/secondaryjoin/
  secondary - the name is pulled from the MetaData of the
  declarative base.
  References: [#1527](https://www.sqlalchemy.org/trac/ticket/1527)
- A column can be added to a joined-table subclass after
  the class has been constructed (i.e. via class-level
  attribute assignment).  The column is added to the underlying
  Table as always, but now the mapper will rebuild its
  “join” to include the new column, instead of raising
  an error about “no such column, use column_property()
  instead”.
  References: [#1523](https://www.sqlalchemy.org/trac/ticket/1523)
- Added examples into the test suite so they get exercised
  regularly and cleaned up a couple deprecation warnings.

## 0.5.5

Released: Mon Jul 13 2009

### general

- unit tests have been migrated from unittest to nose.  See
  README.unittests for information on how to run the tests.
  References: [#970](https://www.sqlalchemy.org/trac/ticket/970)

### orm

- The “foreign_keys” argument of relation() will now propagate
  automatically to the backref in the same way that primaryjoin
  and secondaryjoin do.  For the extremely rare use case where
  the backref of a relation() has intentionally different
  “foreign_keys” configured, both sides now need to be
  configured explicitly (if they do in fact require this setting,
  see the next note…).
- …the only known (and really, really rare) use case where a
  different foreign_keys setting was used on the
  forwards/backwards side, a composite foreign key that
  partially points to its own columns, has been enhanced such
  that the fk->itself aspect of the relation won’t be used to
  determine relation direction.
- Session.mapper is now *deprecated*.
  Call session.add() if you’d like a free-standing object to be
  part of your session.  Otherwise, a DIY version of
  Session.mapper is now documented at
  [https://www.sqlalchemy.org/trac/wiki/UsageRecipes/SessionAwareMapper](https://www.sqlalchemy.org/trac/wiki/UsageRecipes/SessionAwareMapper)
  The method will remain deprecated throughout 0.6.
- Fixed Query being able to join() from individual columns of a
  joined-table subclass entity, i.e.  query(SubClass.foo,
  SubClass.bar).join(<anything>).  In most cases, an error
  “Could not find a FROM clause to join from” would be
  raised. In a few others, the result would be returned in terms
  of the base class rather than the subclass - so applications
  which relied on this erroneous result need to be
  adjusted.
  References: [#1431](https://www.sqlalchemy.org/trac/ticket/1431)
- Fixed a bug involving contains_eager(), which would apply
  itself to a secondary (i.e. lazy) load in a particular rare
  case, producing cartesian products.  improved the targeting of
  query.options() on secondary loads overall.
  References: [#1461](https://www.sqlalchemy.org/trac/ticket/1461)
- Fixed bug introduced in 0.5.4 whereby Composite types fail
  when default-holding columns are flushed.
- Fixed another 0.5.4 bug whereby mutable attributes
  (i.e. PickleType) wouldn’t be deserialized correctly when the
  whole object was serialized.
  References: [#1426](https://www.sqlalchemy.org/trac/ticket/1426)
- Fixed bug whereby session.is_modified() would raise an
  exception if any synonyms were in use.
- Fixed potential memory leak whereby previously pickled objects
  placed back in a session would not be fully garbage collected
  unless the Session were explicitly closed out.
- Fixed bug whereby list-based attributes, like pickletype and
  PGArray, failed to be merged() properly.
- Repaired non-working attributes.set_committed_value function.
- Trimmed the pickle format for InstanceState which should
  further reduce the memory footprint of pickled instances.  The
  format should be backwards compatible with that of 0.5.4 and
  previous.
- sqlalchemy.orm.join and sqlalchemy.orm.outerjoin are now
  added to __all__ in sqlalchemy.orm.*.
  References: [#1463](https://www.sqlalchemy.org/trac/ticket/1463)
- Fixed bug where Query exception raise would fail when
  a too-short composite primary key value were passed to
  get().
  References: [#1458](https://www.sqlalchemy.org/trac/ticket/1458)

### sql

- Removed an obscure feature of execute() (including connection,
  engine, Session) whereby a bindparam() construct can be sent
  as a key to the params dictionary.  This usage is undocumented
  and is at the core of an issue whereby the bindparam() object
  created implicitly by a text() construct may have the same
  hash value as a string placed in the params dictionary and may
  result in an inappropriate match when computing the final bind
  parameters.  Internal checks for this condition would add
  significant latency to the critical task of parameter
  rendering, so the behavior is removed.  This is a backwards
  incompatible change for any application that may have been
  using this feature, however the feature has never been
  documented.

### misc

- Implemented recreate() for StaticPool.

## 0.5.4p2

Released: Tue May 26 2009

### sql

- Repaired the printing of SQL exceptions which are not
  based on parameters or are not executemany() style.

### postgresql

- Deprecated the hardcoded TIMESTAMP function, which when
  used as func.TIMESTAMP(value) would render “TIMESTAMP value”.
  This breaks on some platforms as PostgreSQL doesn’t allow
  bind parameters to be used in this context.  The hard-coded
  uppercase is also inappropriate and there’s lots of other
  PG casts that we’d need to support.  So instead, use
  text constructs i.e. select([“timestamp ‘12/05/09’”]).

## 0.5.4p1

Released: Mon May 18 2009

### orm

- Fixed an attribute error introduced in 0.5.4 which would
  occur when merge() was used with an incomplete object.

## 0.5.4

Released: Sun May 17 2009

### orm

- Significant performance enhancements regarding Sessions/flush()
  in conjunction with large mapper graphs, large numbers of
  objects:
  - Removed all* O(N) scanning behavior from the flush() process,
    i.e. operations that were scanning the full session,
    including an extremely expensive one that was erroneously
    assuming primary key values were changing when this
    was not the case.
    - one edge case remains which may invoke a full scan,
      if an existing primary key attribute is modified
      to a new value.
  - The Session’s “weak referencing” behavior is now *full* -
    no strong references whatsoever are made to a mapped object
    or related items/collections in its __dict__.  Backrefs and
    other cycles in objects no longer affect the Session’s ability
    to lose all references to unmodified objects.  Objects with
    pending changes still are maintained strongly until flush.
    The implementation also improves performance by moving
    the “resurrection” process of garbage collected items
    to only be relevant for mappings that map “mutable”
    attributes (i.e. PickleType, composite attrs).  This removes
    overhead from the gc process and simplifies internal
    behavior.
    If a “mutable” attribute change is the sole change on an object
    which is then dereferenced, the mapper will not have access to
    other attribute state when the UPDATE is issued.  This may present
    itself differently to some MapperExtensions.
    The change also affects the internal attribute API, but not
    the AttributeExtension interface nor any of the publicly
    documented attribute functions.
  - The unit of work no longer generates a graph of “dependency”
    processors for the full graph of mappers during flush(), instead
    creating such processors only for those mappers which represent
    objects with pending changes.  This saves a tremendous number
    of method calls in the context of a large interconnected
    graph of mappers.
  - Cached a wasteful “table sort” operation that previously
    occurred multiple times per flush, also removing significant
    method call count from flush().
  - Other redundant behaviors have been simplified in
    mapper._save_obj().
  References: [#1398](https://www.sqlalchemy.org/trac/ticket/1398)
- Modified query_cls on DynamicAttributeImpl to accept a full
  mixin version of the AppenderQuery, which allows subclassing
  the AppenderMixin.
- The “polymorphic discriminator” column may be part of a
  primary key, and it will be populated with the correct
  discriminator value.
  References: [#1300](https://www.sqlalchemy.org/trac/ticket/1300)
- Fixed the evaluator not being able to evaluate IS NULL clauses.
- Fixed the “set collection” function on “dynamic” relations to
  initiate events correctly.  Previously a collection could only
  be assigned to a pending parent instance, otherwise modified
  events would not be fired correctly.  Set collection is now
  compatible with merge(), fixes.
  References: [#1352](https://www.sqlalchemy.org/trac/ticket/1352)
- Allowed pickling of PropertyOption objects constructed with
  instrumented descriptors; previously, pickle errors would occur
  when pickling an object which was loaded with a descriptor-based
  option, such as query.options(eagerload(MyClass.foo)).
- Lazy loader will not use get() if the “lazy load” SQL clause
  matches the clause used by get(), but contains some parameters
  hardcoded.  Previously the lazy strategy would fail with the
  get().  Ideally get() would be used with the hardcoded
  parameters but this would require further development.
  References: [#1357](https://www.sqlalchemy.org/trac/ticket/1357)
- MapperOptions and other state associated with query.options()
  is no longer bundled within callables associated with each
  lazy/deferred-loading attribute during a load.
  The options are now associated with the instance’s
  state object just once when it’s populated.  This removes
  the need in most cases for per-instance/attribute loader
  objects, improving load speed and memory overhead for
  individual instances.
  References: [#1391](https://www.sqlalchemy.org/trac/ticket/1391)
- Fixed another location where autoflush was interfering
  with session.merge().  autoflush is disabled completely
  for the duration of merge() now.
  References: [#1360](https://www.sqlalchemy.org/trac/ticket/1360)
- Fixed bug which prevented “mutable primary key” dependency
  logic from functioning properly on a one-to-one
  relation().
  References: [#1406](https://www.sqlalchemy.org/trac/ticket/1406)
- Fixed bug in relation(), introduced in 0.5.3,
  whereby a self referential relation
  from a base class to a joined-table subclass would
  not configure correctly.
- Fixed obscure mapper compilation issue when inheriting
  mappers are used which would result in un-initialized
  attributes.
- Fixed documentation for session weak_identity_map -
  the default value is True, indicating a weak
  referencing map in use.
- Fixed a unit of work issue whereby the foreign
  key attribute on an item contained within a collection
  owned by an object being deleted would not be set to
  None if the relation() was self-referential.
  References: [#1376](https://www.sqlalchemy.org/trac/ticket/1376)
- Fixed Query.update() and Query.delete() failures with eagerloaded
  relations.
  References: [#1378](https://www.sqlalchemy.org/trac/ticket/1378)
- It is now an error to specify both columns of a binary primaryjoin
  condition in the foreign_keys or remote_side collection.  Whereas
  previously it was just nonsensical, but would succeed in a
  non-deterministic way.

### sql

- Back-ported the “compiler” extension from SQLA 0.6.  This
  is a standardized interface which allows the creation of custom
  ClauseElement subclasses and compilers.  In particular it’s
  handy as an alternative to text() when you’d like to
  build a construct that has database-specific compilations.
  See the extension docs for details.
- Exception messages are truncated when the list of bound
  parameters is larger than 10, preventing enormous
  multi-page exceptions from filling up screens and logfiles
  for large executemany() statements.
  References: [#1413](https://www.sqlalchemy.org/trac/ticket/1413)
- `sqlalchemy.extract()` is now dialect sensitive and can
  extract components of timestamps idiomatically across the
  supported databases, including SQLite.
- Fixed __repr__() and other _get_colspec() methods on
  ForeignKey constructed from __clause_element__() style
  construct (i.e. declarative columns).
  References: [#1353](https://www.sqlalchemy.org/trac/ticket/1353)

### schema

- Added a quote_schema() method to the IdentifierPreparer class
  so that dialects can override how schemas get handled. This
  enables the MSSQL dialect to treat schemas as multipart
  identifiers, such as ‘database.owner’.

### extensions

- Fixed adding of deferred or other column properties to a
  declarative class.
  References: [#1379](https://www.sqlalchemy.org/trac/ticket/1379)

### mysql

- Reflecting a FOREIGN KEY construct will take into account
  a dotted schema.tablename combination, if the foreign key
  references a table in a remote schema.
  References: [#1405](https://www.sqlalchemy.org/trac/ticket/1405)

### sqlite

- Corrected the SLBoolean type so that it properly treats only 1
  as True.
  References: [#1402](https://www.sqlalchemy.org/trac/ticket/1402)
- Corrected the float type so that it correctly maps to a
  SLFloat type when being reflected.
  References: [#1273](https://www.sqlalchemy.org/trac/ticket/1273)

### mssql

- Modified how savepoint logic works to prevent it from
  stepping on non-savepoint oriented routines. Savepoint
  support is still very experimental.
- Added in reserved words for MSSQL that covers version 2008
  and all prior versions.
  References: [#1310](https://www.sqlalchemy.org/trac/ticket/1310)
- Corrected problem with information schema not working with a
  binary collation based database. Cleaned up information schema
  since it is only used by mssql now.
  References: [#1343](https://www.sqlalchemy.org/trac/ticket/1343)

## 0.5.3

Released: Tue Mar 24 2009

### orm

- The “objects” argument to session.flush() is deprecated.
  State which represents the linkage between a parent and
  child object does not support “flushed” status on
  one side of the link and not the other, so supporting
  this operation leads to misleading results.
  References: [#1315](https://www.sqlalchemy.org/trac/ticket/1315)
- Query now implements __clause_element__() which produces
  its selectable, which means a Query instance can be accepted
  in many SQL expressions, including col.in_(query),
  union(query1, query2), select([foo]).select_from(query),
  etc.
- Query.join() can now construct multiple FROM clauses, if
  needed.  Such as, query(A, B).join(A.x).join(B.y)
  might say SELECT A.*, B.* FROM A JOIN X, B JOIN Y.
  Eager loading can also tack its joins onto those
  multiple FROM clauses.
  References: [#1337](https://www.sqlalchemy.org/trac/ticket/1337)
- Fixed bug in dynamic_loader() where append/remove events
  after construction time were not being propagated to the
  UOW to pick up on flush().
  References: [#1347](https://www.sqlalchemy.org/trac/ticket/1347)
- Fixed bug where column_prefix wasn’t being checked before
  not mapping an attribute that already had class-level
  name present.
- a session.expire() on a particular collection attribute
  will clear any pending backref additions as well, so that
  the next access correctly returns only what was present
  in the database.  Presents some degree of a workaround for, although we are considering removing the
  flush([objects]) feature altogether.
  References: [#1315](https://www.sqlalchemy.org/trac/ticket/1315)
- Session.scalar() now converts raw SQL strings to text()
  the same way Session.execute() does and accepts same
  alternative **kw args.
- improvements to the “determine direction” logic of
  relation() such that the direction of tricky situations
  like mapper(A.join(B)) -> relation-> mapper(B) can be
  determined.
- When flushing partial sets of objects using session.flush([somelist]),
  pending objects which remain pending after the operation won’t
  inadvertently be added as persistent.
  References: [#1306](https://www.sqlalchemy.org/trac/ticket/1306)
- Added “post_configure_attribute” method to InstrumentationManager,
  so that the “listen_for_events.py” example works again.
  References: [#1314](https://www.sqlalchemy.org/trac/ticket/1314)
- a forward and complementing backwards reference which are both
  of the same direction, i.e. ONETOMANY or MANYTOONE,
  is now detected, and an error message is raised.
  Saves crazy CircularDependencyErrors later on.
- Fixed bugs in Query regarding simultaneous selection of
  multiple joined-table inheritance entities with common base
  classes:
  - previously the adaption applied to “B” on
    “A JOIN B” would be erroneously partially applied
    to “A”.
  - comparisons on relations (i.e. A.related==someb)
    were not getting adapted when they should.
  - Other filterings, like
    query(A).join(A.bs).filter(B.foo==’bar’), were erroneously
    adapting “B.foo” as though it were an “A”.
- Fixed adaptation of EXISTS clauses via any(), has(), etc.
  in conjunction with an aliased object on the left and
  of_type() on the right.
  References: [#1325](https://www.sqlalchemy.org/trac/ticket/1325)
- Added an attribute helper method `set_committed_value` in
  sqlalchemy.orm.attributes.  Given an object, attribute name,
  and value, will set the value on the object as part of its
  “committed” state, i.e. state that is understood to have
  been loaded from the database.   Helps with the creation of
  homegrown collection loaders and such.
- Query won’t fail with weakref error when a non-mapper/class
  instrumented descriptor is passed, raises
  “Invalid column expression”.
- Query.group_by() properly takes into account aliasing applied
  to the FROM clause, such as with select_from(), using
  with_polymorphic(), or using from_self().

### sql

- An alias() of a select() will convert to a “scalar subquery”
  when used in an unambiguously scalar context, i.e. it’s used
  in a comparison operation.  This applies to
  the ORM when using query.subquery() as well.
- Fixed missing _label attribute on Function object, others
  when used in a select() with use_labels (such as when used
  in an ORM column_property()).
  References: [#1302](https://www.sqlalchemy.org/trac/ticket/1302)
- anonymous alias names now truncate down to the max length
  allowed by the dialect.  More significant on DBs like
  Oracle with very small character limits.
  References: [#1309](https://www.sqlalchemy.org/trac/ticket/1309)
- the __selectable__() interface has been replaced entirely
  by __clause_element__().
- The per-dialect cache used by TypeEngine to cache
  dialect-specific types is now a WeakKeyDictionary.
  This to prevent dialect objects from
  being referenced forever for an application that
  creates an arbitrarily large number of engines
  or dialects.   There is a small performance penalty
  which will be resolved in 0.6.
  References: [#1299](https://www.sqlalchemy.org/trac/ticket/1299)

### extensions

- Fixed a recursive pickling issue in serializer, triggered
  by an EXISTS or other embedded FROM construct.
- Declarative locates the “inherits” class using a search
  through __bases__, to skip over mixins that are local
  to subclasses.
- Declarative figures out joined-table inheritance primary join
  condition even if “inherits” mapper argument is given
  explicitly.
- Declarative will properly interpret the “foreign_keys” argument
  on a backref() if it’s a string.
- Declarative will accept a table-bound column as a property
  when used in conjunction with __table__, if the column is already
  present in __table__.  The column will be remapped to the given
  key the same way as when added to the mapper() properties dict.

### postgresql

- Index reflection won’t fail when an index with
  multiple expressions is encountered.
- Added PGUuid and PGBit types to
  sqlalchemy.databases.postgres.
  References: [#1327](https://www.sqlalchemy.org/trac/ticket/1327)
- Reflection of unknown PG types won’t crash when those
  types are specified within a domain.
  References: [#1327](https://www.sqlalchemy.org/trac/ticket/1327)

### sqlite

- Fixed SQLite reflection methods so that non-present
  cursor.description, which triggers an auto-cursor
  close, will be detected so that no results doesn’t
  fail on recent versions of pysqlite which raise
  an error when fetchone() called with no rows present.

### mssql

- Preliminary support for pymssql 1.0.1
- Corrected issue on mssql where max_identifier_length was
  not being respected.

## 0.5.2

Released: Sat Jan 24 2009

### orm

- Further refined 0.5.1’s warning about delete-orphan cascade
  placed on a many-to-many relation.   First, the bad news:
  the warning will apply to both many-to-many as well as
  many-to-one relations.  This is necessary since in both
  cases, SQLA does not scan the full set of potential parents
  when determining “orphan” status - for a persistent object
  it only detects an in-python de-association event to establish
  the object as an “orphan”.  Next, the good news: to support
  one-to-one via a foreign key or association table, or to
  support one-to-many via an association table, a new flag
  single_parent=True may be set which indicates objects
  linked to the relation are only meant to have a single parent.
  The relation will raise an error if multiple parent-association
  events occur within Python.
- Adjusted the attribute instrumentation change from 0.5.1 to
  fully establish instrumentation for subclasses where the mapper
  was created after the superclass had already been fully
  instrumented.
  References: [#1292](https://www.sqlalchemy.org/trac/ticket/1292)
- Fixed bug in delete-orphan cascade whereby two one-to-one
  relations from two different parent classes to the same target
  class would prematurely expunge the instance.
- Fixed an eager loading bug whereby self-referential eager
  loading would prevent other eager loads, self referential or not,
  from joining to the parent JOIN properly.  Thanks to Alex K
  for creating a great test case.
- session.expire() and related methods will not expire() unloaded
  deferred attributes.  This prevents them from being needlessly
  loaded when the instance is refreshed.
- query.join()/outerjoin() will now properly join an aliased()
  construct to the existing left side, even if query.from_self()
  or query.select_from(someselectable) has been called.
  References: [#1293](https://www.sqlalchemy.org/trac/ticket/1293)

### sql

- Further fixes to the “percent signs and spaces in column/table
  names” functionality.
  References: [#1284](https://www.sqlalchemy.org/trac/ticket/1284)

### mssql

- Restored convert_unicode handling. Results were being passed
  on through without conversion.
  References: [#1291](https://www.sqlalchemy.org/trac/ticket/1291)
- Really fixing the decimal handling this time..
  References: [#1282](https://www.sqlalchemy.org/trac/ticket/1282)
- Modified table reflection code to use only kwargs when
  constructing tables.

## 0.5.1

Released: Sat Jan 17 2009

### orm

- Removed an internal join cache which could potentially leak
  memory when issuing query.join() repeatedly to ad-hoc
  selectables.
- The “clear()”, “save()”, “update()”, “save_or_update()”
  Session methods have been deprecated, replaced by
  “expunge_all()” and “add()”.  “expunge_all()” has also
  been added to ScopedSession.
- Modernized the “no mapped table” exception and added a more
  explicit __table__/__tablename__ exception to declarative.
- Concrete inheriting mappers now instrument attributes which
  are inherited from the superclass, but are not defined for
  the concrete mapper itself, with an InstrumentedAttribute that
  issues a descriptive error when accessed.
  References: [#1237](https://www.sqlalchemy.org/trac/ticket/1237)
- Added a new relation() keyword back_populates. This
  allows configuration of backreferences using explicit
  relations. This is required when creating
  bidirectional relations between a hierarchy of concrete
  mappers and another class.
  References: [#1237](https://www.sqlalchemy.org/trac/ticket/1237), [#781](https://www.sqlalchemy.org/trac/ticket/781)
- Test coverage added for relation() objects specified on
  concrete mappers.
  References: [#1237](https://www.sqlalchemy.org/trac/ticket/1237)
- Query.from_self() as well as query.subquery() both disable
  the rendering of eager joins inside the subquery produced.
  The “disable all eager joins” feature is available publicly
  via a new query.enable_eagerloads() generative.
  References: [#1276](https://www.sqlalchemy.org/trac/ticket/1276)
- Added a rudimental series of set operations to Query that
  receive Query objects as arguments, including union(),
  union_all(), intersect(), except_(), intersect_all(),
  except_all().  See the API documentation for
  Query.union() for examples.
- Fixed bug that prevented Query.join() and eagerloads from
  attaching to a query that selected from a union or aliased union.
- A short documentation example added for bidirectional
  relations specified on concrete mappers.
  References: [#1237](https://www.sqlalchemy.org/trac/ticket/1237)
- Mappers now instrument class attributes upon construction
  with the final InstrumentedAttribute object which remains
  persistent. The _CompileOnAttr/__getattribute__()
  methodology has been removed. The net effect is that
  Column-based mapped class attributes can now be used fully
  at the class level without invoking a mapper compilation
  operation, greatly simplifying typical usage patterns
  within declarative.
  References: [#1269](https://www.sqlalchemy.org/trac/ticket/1269)
- ColumnProperty (and front-end helpers such as `deferred`) no
  longer ignores unknown **keyword arguments.
- Fixed a bug with the unitofwork’s “row switch” mechanism,
  i.e. the conversion of INSERT/DELETE into an UPDATE, when
  combined with joined-table inheritance and an object
  which contained no defined values for the child table where
  an UPDATE with no SET clause would be rendered.
- Using delete-orphan on a many-to-many relation is deprecated.
  This produces misleading or erroneous results since SQLA does
  not retrieve the full list of “parents” for m2m.  To get delete-orphan
  behavior with an m2m table, use an explicit association class
  so that the individual association row is treated as a parent.
  References: [#1281](https://www.sqlalchemy.org/trac/ticket/1281)
- delete-orphan cascade always requires delete cascade.  Specifying
  delete-orphan without delete now raises a deprecation warning.
  References: [#1281](https://www.sqlalchemy.org/trac/ticket/1281)

### sql

- Improved the methodology to handling percent signs in column
  names from.  Added more tests.  MySQL and
  PostgreSQL dialects still do not issue correct CREATE TABLE
  statements for identifiers with percent signs in them.
  References: [#1256](https://www.sqlalchemy.org/trac/ticket/1256)

### schema

- Index now accepts column-oriented InstrumentedAttributes
  (i.e. column-based mapped class attributes) as column
  arguments.
  References: [#1214](https://www.sqlalchemy.org/trac/ticket/1214)
- Column with no name (as in declarative) won’t raise a
  NoneType error when its string output is requested
  (such as in a stack trace).
- Fixed bug when overriding a Column with a ForeignKey
  on a reflected table, where derived columns (i.e. the
  “virtual” columns of a select, etc.) would inadvertently
  call upon schema-level cleanup logic intended only
  for the original column.
  References: [#1278](https://www.sqlalchemy.org/trac/ticket/1278)

### mysql

- Added the missing keywords from MySQL 4.1 so they get escaped
  properly.

### mssql

- Corrected handling of large decimal values with more robust
  tests. Removed string manipulation on floats.
  References: [#1280](https://www.sqlalchemy.org/trac/ticket/1280)
- Modified the do_begin handling in mssql to use the Cursor not
  the Connection so it is DBAPI compatible.
- Corrected SAVEPOINT support on adodbapi by changing the
  handling of savepoint_release, which is unsupported on mssql.

### misc

- Can now specify Column objects on subclasses which have no
  table of their own (i.e. use single table inheritance).
  The columns will be appended to the base table, but only
  mapped by the subclass.
- For both joined and single inheriting subclasses, the subclass
  will only map those columns which are already mapped on the
  superclass and those explicit on the subclass.  Other
  columns that are present on the Table will be excluded
  from the mapping by default, which can be disabled
  by passing a blank exclude_properties collection to the
  __mapper_args__.  This is so that single-inheriting
  classes which define their own columns are the only classes
  to map those columns.   The effect is actually a more organized
  mapping than you’d normally get with explicit mapper()
  calls unless you set up the exclude_properties arguments
  explicitly.
- It’s an error to add new Column objects to a declarative class
  that specified an existing table using __table__.

## 0.5.0

Released: Tue Jan 06 2009

### general

- Documentation has been converted to Sphinx.  In particular,
  the generated API documentation has been constructed into a
  full blown “API Reference” section which organizes editorial
  documentation combined with generated docstrings.  Cross
  linking between sections and API docs are vastly improved, a
  javascript-powered search feature is provided, and a full
  index of all classes, functions and members is provided.
- setup.py now imports setuptools only optionally.  If not
  present, distutils is used.  The new “pip” installer is
  recommended over easy_install as it installs in a more
  simplified way.
- added an extremely basic illustration of a PostGIS integration
  to the examples folder.

### orm

- Query.with_polymorphic() now accepts a third argument
  “discriminator” which will replace the value of
  mapper.polymorphic_on for that query.  Mappers themselves no
  longer require polymorphic_on to be set, even if the mapper
  has a polymorphic_identity.  When not set, the mapper will
  load non-polymorphically by default. Together, these two
  features allow a non-polymorphic concrete inheritance setup to
  use polymorphic loading on a per-query basis, since concrete
  setups are prone to many issues when used polymorphically in
  all cases.
- dynamic_loader accepts a query_class= to customize the Query
  classes used for both the dynamic collection and the queries
  built from it.
- query.order_by() accepts None which will remove any pending
  order_by state from the query, as well as cancel out any
  mapper/relation configured ordering. This is primarily useful
  for overriding the ordering specified on a dynamic_loader().
  References: [#1079](https://www.sqlalchemy.org/trac/ticket/1079)
- Exceptions raised during compile_mappers() are now preserved
  to provide “sticky behavior” - if a hasattr() call on a
  pre-compiled mapped attribute triggers a failing compile and
  suppresses the exception, subsequent compilation is blocked
  and the exception will be reiterated on the next compile()
  call.  This issue occurs frequently when using declarative.
- property.of_type() is now recognized on a single-table
  inheriting target, when used in the context of
  prop.of_type(..).any()/has(), as well as
  query.join(prop.of_type(…)).
- query.join() raises an error when the target of the join
  doesn’t match the property-based attribute - while it’s
  unlikely anyone is doing this, the SQLAlchemy author was
  guilty of this particular loosey-goosey behavior.
- Fixed bug when using weak_instance_map=False where modified
  events would not be intercepted for a flush().
  References: [#1272](https://www.sqlalchemy.org/trac/ticket/1272)
- Fixed some deep “column correspondence” issues which could
  impact a Query made against a selectable containing multiple
  versions of the same table, as well as unions and similar
  which contained the same table columns in different column
  positions at different levels.
  References: [#1268](https://www.sqlalchemy.org/trac/ticket/1268)
- Custom comparator classes used in conjunction with
  column_property(), relation() etc. can define new comparison
  methods on the Comparator, which will become available via
  __getattr__() on the InstrumentedAttribute.  In the case of
  synonym() or comparable_property(), attributes are resolved
  first on the user-defined descriptor, then on the user-defined
  comparator.
- Added ScopedSession.is_active accessor.
  References: [#976](https://www.sqlalchemy.org/trac/ticket/976)
- Can pass mapped attributes and column objects as keys to
  query.update({}).
  References: [#1262](https://www.sqlalchemy.org/trac/ticket/1262)
- Mapped attributes passed to the values() of an expression
  level insert() or update() will use the keys of the mapped
  columns, not that of the mapped attribute.
- Corrected problem with Query.delete() and Query.update() not
  working properly with bind parameters.
  References: [#1242](https://www.sqlalchemy.org/trac/ticket/1242)
- Query.select_from(), from_statement() ensure that the given
  argument is a FromClause, or Text/Select/Union, respectively.
- Query() can be passed a “composite” attribute as a column
  expression and it will be expanded.  Somewhat related to.
  References: [#1253](https://www.sqlalchemy.org/trac/ticket/1253)
- Query() is a little more robust when passed various column
  expressions such as strings, clauselists, text() constructs
  (which may mean it just raises an error more nicely).
- first() works as expected with Query.from_statement().
- Fixed bug introduced in 0.5rc4 involving eager loading not
  functioning for properties which were added to a mapper
  post-compile using add_property() or equivalent.
- Fixed bug where many-to-many relation() with viewonly=True
  would not correctly reference the link between
  secondary->remote.
- Duplicate items in a list-based collection will be maintained
  when issuing INSERTs to a “secondary” table in a many-to-many
  relation.  Assuming the m2m table has a unique or primary key
  constraint on it, this will raise the expected constraint
  violation instead of silently dropping the duplicate
  entries. Note that the old behavior remains for a one-to-many
  relation since collection entries in that case don’t result in
  INSERT statements and SQLA doesn’t manually police
  collections.
  References: [#1232](https://www.sqlalchemy.org/trac/ticket/1232)
- Query.add_column() can accept FromClause objects in the same
  manner as session.query() can.
- Comparison of many-to-one relation to NULL is properly
  converted to IS NOT NULL based on not_().
- Extra checks added to ensure explicit
  primaryjoin/secondaryjoin are ClauseElement instances, to
  prevent more confusing errors later on.
  References: [#1087](https://www.sqlalchemy.org/trac/ticket/1087)
- Improved mapper() check for non-class classes.
  References: [#1236](https://www.sqlalchemy.org/trac/ticket/1236)
- comparator_factory argument is now documented and supported by
  all MapperProperty types, including column_property(),
  relation(), backref(), and synonym().
  References: [#5051](https://www.sqlalchemy.org/trac/ticket/5051)
- Changed the name of PropertyLoader to RelationProperty, to be
  consistent with all the other names.  PropertyLoader is still
  present as a synonym.
- fixed “double iter()” call causing bus errors in shard API,
  removed errant result.close() left over from the 0.4
  version.
  References: [#1099](https://www.sqlalchemy.org/trac/ticket/1099), [#1228](https://www.sqlalchemy.org/trac/ticket/1228)
- made Session.merge cascades not trigger autoflush.  Fixes
  merged instances getting prematurely inserted with missing
  values.
- Two fixes to help prevent out-of-band columns from being
  rendered in polymorphic_union inheritance scenarios (which
  then causes extra tables to be rendered in the FROM clause
  causing cartesian products):
  > - improvements to “column adaption” for a->b->c inheritance
  >   situations to better locate columns that are related to
  >   one another via multiple levels of indirection, rather
  >   than rendering the non-adapted column.
  > - the “polymorphic discriminator” column is only rendered
  >   for the actual mapper being queried against. The column
  >   won’t be “pulled in” from a subclass or superclass mapper
  >   since it’s not needed.
- Fixed shard_id argument on ShardedSession.execute().
  References: [#1072](https://www.sqlalchemy.org/trac/ticket/1072)

### sql

- RowProxy objects can be used in place of dictionary arguments
  sent to connection.execute() and friends.
  References: [#935](https://www.sqlalchemy.org/trac/ticket/935)
- Columns can again contain percent signs within their
  names.
  References: [#1256](https://www.sqlalchemy.org/trac/ticket/1256)
- sqlalchemy.sql.expression.Function is now a public class.  It
  can be subclassed to provide user-defined SQL functions in an
  imperative style, including with pre-established behaviors.
  The postgis.py example illustrates one usage of this.
- PickleType now favors == comparison by default, if the
  incoming object (such as a dict) implements __eq__().  If the
  object does not implement __eq__() and mutable=True, a
  deprecation warning is raised.
- Fixed the import weirdness in sqlalchemy.sql to not export
  __names__.
  References: [#1215](https://www.sqlalchemy.org/trac/ticket/1215)
- Using the same ForeignKey object repeatedly raises an error
  instead of silently failing later.
  References: [#1238](https://www.sqlalchemy.org/trac/ticket/1238)
- Added NotImplementedError for params() method on
  Insert/Update/Delete constructs.  These items currently don’t
  support this functionality, which also would be a little
  misleading compared to values().
- Reflected foreign keys will properly locate their referenced
  column, even if the column was given a “key” attribute
  different from the reflected name.  This is achieved via a new
  flag on ForeignKey/ForeignKeyConstraint called “link_to_name”,
  if True means the given name is the referred-to column’s name,
  not its assigned key.
  References: [#650](https://www.sqlalchemy.org/trac/ticket/650)
- select() can accept a ClauseList as a column in the same way
  as a Table or other selectable and the interior expressions
  will be used as column elements.
  References: [#1253](https://www.sqlalchemy.org/trac/ticket/1253)
- the “passive” flag on session.is_modified() is correctly
  propagated to the attribute manager.
- union() and union_all() will not whack any order_by() that has
  been applied to the select()s inside.  If you union() a
  select() with order_by() (presumably to support LIMIT/OFFSET),
  you should also call self_group() on it to apply parenthesis.

### mysql

- ”%” signs in text() constructs are automatically escaped to
  “%%”.  Because of the backwards incompatible nature of this
  change, a warning is emitted if ‘%%’ is detected in the
  string.
- Fixed bug in exception raise when FK columns not present
  during reflection.
  References: [#1241](https://www.sqlalchemy.org/trac/ticket/1241)
- Fixed bug involving reflection of a remote-schema table with a
  foreign key ref to another table in that schema.

### sqlite

- Table reflection now stores the actual DefaultClause value for
  the column.
  References: [#1266](https://www.sqlalchemy.org/trac/ticket/1266)
- bugfixes, behavioral changes

### mssql

- Added in a new MSGenericBinary type. This maps to the Binary
  type so it can implement the specialized behavior of treating
  length specified types as fixed-width Binary types and
  non-length types as an unbound variable length Binary type.
- Added in new types: MSVarBinary and MSImage.
  References: [#1249](https://www.sqlalchemy.org/trac/ticket/1249)
- Added in the MSReal, MSNText, MSSmallDateTime, MSTime,
  MSDateTimeOffset, and MSDateTime2 types
- Refactored the Date/Time types. The `smalldatetime` data
  type no longer truncates to a date only, and will now be
  mapped to the MSSmallDateTime type.
  References: [#1254](https://www.sqlalchemy.org/trac/ticket/1254)
- Corrected an issue with Numerics to accept an int.
- Mapped `char_length` to the `LEN()` function.
- If an `INSERT` includes a subselect the `INSERT` is
  converted from an `INSERT INTO VALUES` construct to a
  `INSERT INTO SELECT` construct.
- If the column is part of a `primary_key` it will be `NOT
  NULL` since MSSQL doesn’t allow `NULL` in primary_key
  columns.
- `MSBinary` now returns a `BINARY` instead of an
  `IMAGE`. This is a backwards incompatible change in that
  `BINARY` is a fixed length data type whereas `IMAGE` is a
  variable length data type.
  References: [#1249](https://www.sqlalchemy.org/trac/ticket/1249)
- `get_default_schema_name` is now reflected from the database
  based on the user’s default schema. This only works with MSSQL
  2005 and later.
  References: [#1258](https://www.sqlalchemy.org/trac/ticket/1258)
- Added collation support through the use of a new collation
  argument. This is supported on the following types: char,
  nchar, varchar, nvarchar, text, ntext.
  References: [#1248](https://www.sqlalchemy.org/trac/ticket/1248)
- Changes to the connection string parameters favor DSN as the
  default specification for pyodbc. See the mssql.py docstring
  for detailed usage instructions.
- Added experimental support of savepoints. It currently does
  not work fully with sessions.
- Support for three levels of column nullability: NULL, NOT
  NULL, and the database’s configured default.  The default
  Column configuration (nullable=True) will now generate NULL in
  the DDL. Previously no specification was emitted and the
  database default would take effect (usually NULL, but not
  always).  To explicitly request the database default,
  configure columns with nullable=None and no specification will
  be emitted in DDL. This is backwards incompatible
  behavior.
  References: [#1243](https://www.sqlalchemy.org/trac/ticket/1243)

### oracle

- Adjusted the format of create_xid() to repair two-phase
  commit.  We now have field reports of Oracle two-phase commit
  working properly with this change.
- Added OracleNVarchar type, produces NVARCHAR2, and also
  subclasses Unicode so that convert_unicode=True by default.
  NVARCHAR2 reflects into this type automatically so these
  columns pass unicode on a reflected table with no explicit
  convert_unicode=True flags.
  References: [#1233](https://www.sqlalchemy.org/trac/ticket/1233)
- Fixed bug which was preventing out params of certain types
  from being received; thanks a ton to huddlej at wwu.edu !
  References: [#1265](https://www.sqlalchemy.org/trac/ticket/1265)

### misc

- Added a new description_encoding attribute on the dialect that
  is used for encoding the column name when processing the
  metadata. This usually defaults to utf-8.
- Connection.invalidate() checks for closed status to avoid
  attribute errors.
  References: [#1246](https://www.sqlalchemy.org/trac/ticket/1246)
- NullPool supports reconnect on failure behavior.
  References: [#1094](https://www.sqlalchemy.org/trac/ticket/1094)
- Added a mutex for the initial pool creation when using
  pool.manage(dbapi).  This prevents a minor case of “dogpile”
  behavior which would otherwise occur upon a heavy load
  startup.
  References: [#799](https://www.sqlalchemy.org/trac/ticket/799)
- _execute_clauseelement() goes back to being a private method.
  Subclassing Connection is not needed now that ConnectionProxy
  is available.
- Tickets.
  References: [#1149](https://www.sqlalchemy.org/trac/ticket/1149), [#1200](https://www.sqlalchemy.org/trac/ticket/1200)
- Added note about create_session() defaults.
- Added section about metadata.reflect().
- Updated TypeDecorator section.
- Rewrote the “threadlocal” strategy section of the docs due to
  recent confusion over this feature.
- Removed badly out of date ‘polymorphic_fetch’ and
  ‘select_table’ docs from inheritance, reworked the second half
  of “joined table inheritance”.
- Documented comparator_factory kwarg, added new doc section
  “Custom Comparators”.
- ”%” signs in text() constructs are automatically escaped to
  “%%”.  Because of the backwards incompatible nature of this
  change, a warning is emitted if ‘%%’ is detected in the
  string.
  References: [#1267](https://www.sqlalchemy.org/trac/ticket/1267)
- Calling alias.execute() in conjunction with
  server_side_cursors won’t raise AttributeError.
- Added Index reflection support to PostgreSQL, using a great
  patch we long neglected, submitted by Ken
  Kuhlman.
  References: [#714](https://www.sqlalchemy.org/trac/ticket/714)
- The association proxy properties are make themselves available
  at the class level, e.g. MyClass.aproxy.  Previously this
  evaluated to None.
- The full list of arguments accepted as string by backref()
  includes ‘primaryjoin’, ‘secondaryjoin’, ‘secondary’,
  ‘foreign_keys’, ‘remote_side’, ‘order_by’.

## 0.5.0rc4

Released: Fri Nov 14 2008

### general

- global “propagate”->”propagate” change.

### orm

- Query.count() has been enhanced to do the “right thing” in a
  wider variety of cases. It can now count multiple-entity
  queries, as well as column-based queries. Note that this means
  if you say query(A, B).count() without any joining criterion,
  it’s going to count the cartesian product of A*B. Any query
  which is against column-based entities will automatically
  issue “SELECT count(1) FROM (SELECT…)” so that the real
  rowcount is returned, meaning a query such as
  query(func.count(A.name)).count() will return a value of one,
  since that query would return one row.
- Lots of performance tuning.  A rough guesstimate over various
  ORM operations places it 10% faster over 0.5.0rc3, 25-30% over
  0.4.8.
- bugfixes and behavioral changes
- Adjustments to the enhanced garbage collection on
  InstanceState to better guard against errors due to lost
  state.
- Query.get() returns a more informative error message when
  executed against multiple entities.
  References: [#1220](https://www.sqlalchemy.org/trac/ticket/1220)
- Restored NotImplementedError on Cls.relation.in_()
  References: [#1140](https://www.sqlalchemy.org/trac/ticket/1140), [#1221](https://www.sqlalchemy.org/trac/ticket/1221)
- Fixed PendingDeprecationWarning involving order_by parameter
  on relation().
  References: [#1226](https://www.sqlalchemy.org/trac/ticket/1226)

### sql

- Removed the ‘properties’ attribute of the Connection object,
  Connection.info should be used.
- Restored “active rowcount” fetch before ResultProxy autocloses
  the cursor.  This was removed in 0.5rc3.
- Rearranged the load_dialect_impl() method in TypeDecorator
  such that it will take effect even if the user-defined
  TypeDecorator uses another TypeDecorator as its impl.

### mssql

- Lots of cleanup and fixes to correct problems with limit and
  offset.
- Correct situation where subqueries as part of a binary
  expression need to be translated to use the IN and NOT IN
  syntax.
- Fixed E Notation issue that prevented the ability to insert
  decimal values less than 1E-6.
  References: [#1216](https://www.sqlalchemy.org/trac/ticket/1216)
- Corrected problems with reflection when dealing with schemas,
  particularly when those schemas are the default
  schema.
  References: [#1217](https://www.sqlalchemy.org/trac/ticket/1217)
- Corrected problem with casting a zero length item to a
  varchar. It now correctly adjusts the CAST.

### misc

- Added support for Currency type.
- Functions were not return their result.
  References: [#1017](https://www.sqlalchemy.org/trac/ticket/1017)
- Corrected problem with joins. Access only support LEFT OUTER
  or INNER not just JOIN by itself.
  References: [#1017](https://www.sqlalchemy.org/trac/ticket/1017)
- Can now use a custom “inherit_condition” in __mapper_args__
  when using declarative.
- fixed string-based “remote_side”, “order_by” and others not
  propagating correctly when used in backref().

## 0.5.0rc3

Released: Fri Nov 07 2008

### orm

- Added two new hooks to SessionExtension: after_bulk_delete()
  and after_bulk_update().  after_bulk_delete() is called after
  a bulk delete() operation on a query. after_bulk_update() is
  called after a bulk update() operation on a query.
- ”not equals” comparisons of simple many-to-one relation to an
  instance will not drop into an EXISTS clause and will compare
  foreign key columns instead.
- Removed not-really-working use cases of comparing a collection
  to an iterable. Use contains() to test for collection
  membership.
- Improved the behavior of aliased() objects such that they more
  accurately adapt the expressions generated, which helps
  particularly with self-referential comparisons.
  References: [#1171](https://www.sqlalchemy.org/trac/ticket/1171)
- Fixed bug involving primaryjoin/secondaryjoin conditions
  constructed from class-bound attributes (as often occurs when
  using declarative), which later would be inappropriately
  aliased by Query, particularly with the various EXISTS based
  comparators.
- Fixed bug when using multiple query.join() with an
  aliased-bound descriptor which would lose the left alias.
- Improved weakref identity map memory management to no longer
  require mutexing, resurrects garbage collected instance on a
  lazy basis for an InstanceState with pending changes.
- InstanceState object now removes circular references to itself
  upon disposal to keep it outside of cyclic garbage collection.
- relation() won’t hide unrelated ForeignKey errors inside of
  the “please specify primaryjoin” message when determining join
  condition.
- Fixed bug in Query involving order_by() in conjunction with
  multiple aliases of the same class (will add tests in)
  References: [#1218](https://www.sqlalchemy.org/trac/ticket/1218)
- When using Query.join() with an explicit clause for the ON
  clause, the clause will be aliased in terms of the left side
  of the join, allowing scenarios like query(Source).
  from_self().join((Dest, Source.id==Dest.source_id)) to work
  properly.
- polymorphic_union() function respects the “key” of each Column
  if they differ from the column’s name.
- Repaired support for “passive-deletes” on a many-to-one
  relation() with “delete” cascade.
  References: [#1183](https://www.sqlalchemy.org/trac/ticket/1183)
- Fixed bug in composite types which prevented a primary-key
  composite type from being mutated.
  References: [#1213](https://www.sqlalchemy.org/trac/ticket/1213)
- Added more granularity to internal attribute access, such that
  cascade and flush operations will not initialize unloaded
  attributes and collections, leaving them intact for a
  lazy-load later on. Backref events still initialize attributes
  and collections for pending instances.
  References: [#1202](https://www.sqlalchemy.org/trac/ticket/1202)

### sql

- SQL compiler optimizations and complexity reduction. The call
  count for compiling a typical select() construct is 20% less
  versus 0.5.0rc2.
- Dialects can now generate label names of adjustable
  length. Pass in the argument “label_length=<value>” to
  create_engine() to adjust how many characters max will be
  present in dynamically generated column labels, i.e.
  “somecolumn AS somelabel”. Any value less than 6 will result
  in a label of minimal size, consisting of an underscore and a
  numeric counter. The compiler uses the value of
  dialect.max_identifier_length as a default.
  References: [#1211](https://www.sqlalchemy.org/trac/ticket/1211)
- Simplified the check for ResultProxy “autoclose without
  results” to be based solely on presence of
  cursor.description. All the regexp-based guessing about
  statements returning rows has been removed.
  References: [#1212](https://www.sqlalchemy.org/trac/ticket/1212)
- Direct execution of a union() construct will properly set up
  result-row processing.
  References: [#1194](https://www.sqlalchemy.org/trac/ticket/1194)
- The internal notion of an “OID” or “ROWID” column has been
  removed. It’s basically not used by any dialect, and the
  possibility of its usage with psycopg2’s cursor.lastrowid is
  basically gone now that INSERT..RETURNING is available.
- Removed “default_order_by()” method on all FromClause objects.
- Repaired the table.tometadata() method so that a passed-in
  schema argument is propagated to ForeignKey constructs.
- Slightly changed behavior of IN operator for comparing to
  empty collections. Now results in inequality comparison
  against self. More portable, but breaks with stored procedures
  that aren’t pure functions.

### mysql

- Fixed foreign key reflection in the edge case where a Table’s
  explicit schema= is the same as the schema (database) the
  connection is attached to.
- No longer expects include_columns in table reflection to be
  lower case.

### oracle

- Wrote a docstring for Oracle dialect. Apparently that Ohloh
  “few source code comments” label is starting to string :).
- Removed FIRST_ROWS() optimize flag when using LIMIT/OFFSET,
  can be re-enabled with optimize_limits=True create_engine()
  flag.
  References: [#536](https://www.sqlalchemy.org/trac/ticket/536)
- bugfixes and behavioral changes
- Setting the auto_convert_lobs to False on create_engine() will
  also instruct the OracleBinary type to return the cx_oracle
  LOB object unchanged.

### misc

- Added a new extension sqlalchemy.ext.serializer.  Provides
  Serializer/Deserializer “classes” which mirror
  Pickle/Unpickle, as well as dumps() and loads(). This
  serializer implements an “external object” pickler which keeps
  key context-sensitive objects, including engines, sessions,
  metadata, Tables/Columns, and mappers, outside of the pickle
  stream, and can later restore the pickle using any
  engine/metadata/session provider. This is used not for
  pickling regular object instances, which are pickleable
  without any special logic, but for pickling expression objects
  and full Query objects, such that all mapper/engine/session
  dependencies can be restored at unpickle time.
- Fixed bug preventing declarative-bound “column” objects from
  being used in column_mapped_collection().
  References: [#1174](https://www.sqlalchemy.org/trac/ticket/1174)
- util.flatten_iterator() func doesn’t interpret strings with
  __iter__() methods as iterators, such as in pypy.
  References: [#1077](https://www.sqlalchemy.org/trac/ticket/1077)

## 0.5.0rc2

Released: Sun Oct 12 2008

### orm

- Fixed bug involving read/write relation()s that contain
  literal or other non-column expressions within their
  primaryjoin condition equated to a foreign key column.
- ”non-batch” mode in mapper(), a feature which allows mapper
  extension methods to be called as each instance is
  updated/inserted, now honors the insert order of the objects
  given.
- Fixed RLock-related bug in mapper which could deadlock upon
  reentrant mapper compile() calls, something that occurs when
  using declarative constructs inside of ForeignKey objects.
- ScopedSession.query_property now accepts a query_cls factory,
  overriding the session’s configured query_cls.
- Fixed shared state bug interfering with ScopedSession.mapper’s
  ability to apply default __init__ implementations on object
  subclasses.
- Fixed up slices on Query (i.e. query[x:y]) to work properly
  for zero length slices, slices with None on either end.
  References: [#1177](https://www.sqlalchemy.org/trac/ticket/1177)
- Added an example illustrating Celko’s “nested sets” as a
  SQLA mapping.
- contains_eager() with an alias argument works even when
  the alias is embedded in a SELECT, as when sent to the
  Query via query.select_from().
- contains_eager() usage is now compatible with a Query that
  also contains a regular eager load and limit/offset, in that
  the columns are added to the Query-generated subquery.
  References: [#1180](https://www.sqlalchemy.org/trac/ticket/1180)
- session.execute() will execute a Sequence object passed to
  it (regression from 0.4).
- Removed the “raiseerror” keyword argument from object_mapper()
  and class_mapper().  These functions raise in all cases
  if the given class/instance is not mapped.
- Fixed session.transaction.commit() on a autocommit=False
  session not starting a new transaction.
- Some adjustments to Session.identity_map’s weak referencing
  behavior to reduce asynchronous GC side effects.
- Adjustment to Session’s post-flush accounting of newly
  “clean” objects to better protect against operating on
  objects as they’re asynchronously gc’ed.
  References: [#1182](https://www.sqlalchemy.org/trac/ticket/1182)

### sql

- column.in_(someselect) can now be used as a columns-clause
  expression without the subquery bleeding into the FROM clause
  References: [#1074](https://www.sqlalchemy.org/trac/ticket/1074)

### mysql

- Temporary tables are now reflectable.

### sqlite

- Overhauled SQLite date/time bind/result processing to use
  regular expressions and format strings, rather than
  strptime/strftime, to generically support pre-1900 dates,
  dates with microseconds.
  References: [#968](https://www.sqlalchemy.org/trac/ticket/968)
- String’s (and Unicode’s, UnicodeText’s, etc.) convert_unicode
  logic disabled in the sqlite dialect, to adjust for pysqlite
  2.5.0’s new requirement that only Python unicode objects are
  accepted;
  [http://web.archive.org/web/20090614054912/https://itsystementwicklung.de/pipermail/list-pysqlite/2008-March/000018.html](http://web.archive.org/web/20090614054912/https://itsystementwicklung.de/pipermail/list-pysqlite/2008-March/000018.html)

### oracle

- Oracle will detect string-based statements which contain
  comments at the front before a SELECT as SELECT statements.
  References: [#1187](https://www.sqlalchemy.org/trac/ticket/1187)

## 0.5.0rc1

Released: Thu Sep 11 2008

### orm

- Query now has delete() and update(values) methods. This allows
  to perform bulk deletes/updates with the Query object.
- The RowTuple object returned by Query(*cols) now features
  keynames which prefer mapped attribute names over column keys,
  column keys over column names, i.e.  Query(Class.foo,
  Class.bar) will have names “foo” and “bar” even if those are
  not the names of the underlying Column objects.  Direct Column
  objects such as Query(table.c.col) will return the “key”
  attribute of the Column.
- Added scalar() and value() methods to Query, each return a
  single scalar value.  scalar() takes no arguments and is
  roughly equivalent to first()[0], value()
  takes a single column expression and is roughly equivalent to
  values(expr).next()[0].
- Improved the determination of the FROM clause when placing SQL
  expressions in the query() list of entities.  In particular
  scalar subqueries should not “leak” their inner FROM objects
  out into the enclosing query.
- Joins along a relation() from a mapped class to a mapped
  subclass, where the mapped subclass is configured with single
  table inheritance, will include an IN clause which limits the
  subtypes of the joined class to those requested, within the ON
  clause of the join.  This takes effect for eager load joins as
  well as query.join().  Note that in some scenarios the IN
  clause will appear in the WHERE clause of the query as well
  since this discrimination has multiple trigger points.
- AttributeExtension has been refined such that the event
  is fired before the mutation actually occurs.  Additionally,
  the append() and set() methods must now return the given value,
  which is used as the value to be used in the mutation operation.
  This allows creation of validating AttributeListeners which
  raise before the action actually occurs, and which can change
  the given value into something else before its used.
- column_property(), composite_property(), and relation() now
  accept a single or list of AttributeExtensions using the
  “extension” keyword argument.
- query.order_by().get() silently drops the “ORDER BY” from
  the query issued by GET but does not raise an exception.
- Added a Validator AttributeExtension, as well as a
  @validates decorator which is used in a similar fashion
  as @reconstructor, and marks a method as validating
  one or more mapped attributes.
- class.someprop.in_() raises NotImplementedError pending the
  implementation of “in_” for relation
  References: [#1140](https://www.sqlalchemy.org/trac/ticket/1140)
- Fixed primary key update for many-to-many collections where
  the collection had not been loaded yet
  References: [#1127](https://www.sqlalchemy.org/trac/ticket/1127)
- Fixed bug whereby deferred() columns with a group in conjunction
  with an otherwise unrelated synonym() would produce
  an AttributeError during deferred load.
- The before_flush() hook on SessionExtension takes place before
  the list of new/dirty/deleted is calculated for the final
  time, allowing routines within before_flush() to further
  change the state of the Session before the flush proceeds.
  References: [#1128](https://www.sqlalchemy.org/trac/ticket/1128)
- The “extension” argument to Session and others can now
  optionally be a list, supporting events sent to multiple
  SessionExtension instances.  Session places SessionExtensions
  in Session.extensions.
- Reentrant calls to flush() raise an error.  This also serves
  as a rudimentary, but not foolproof, check against concurrent
  calls to Session.flush().
- Improved the behavior of query.join() when joining to
  joined-table inheritance subclasses, using explicit join
  criteria (i.e. not on a relation).
- @orm.attributes.reconstitute and
  MapperExtension.reconstitute have been renamed to
  @orm.reconstructor and MapperExtension.reconstruct_instance
- Fixed @reconstructor hook for subclasses which inherit from a
  base class.
  References: [#1129](https://www.sqlalchemy.org/trac/ticket/1129)
- The composite() property type now supports a
  __set_composite_values__() method on the composite class which
  is required if the class represents state using attribute
  names other than the column’s keynames; default-generated
  values now get populated properly upon flush.  Also,
  composites with attributes set to None compare correctly.
  References: [#1132](https://www.sqlalchemy.org/trac/ticket/1132)
- The 3-tuple of iterables returned by attributes.get_history()
  may now be a mix of lists and tuples.  (Previously members
  were always lists.)
- Fixed bug whereby changing a primary key attribute on an
  entity where the attribute’s previous value had been expired
  would produce an error upon flush().
  References: [#1151](https://www.sqlalchemy.org/trac/ticket/1151)
- Fixed custom instrumentation bug whereby get_instance_dict()
  was not called for newly constructed instances not loaded
  by the ORM.
- Session.delete() adds the given object to the session if
  not already present.  This was a regression bug from 0.4.
  References: [#1150](https://www.sqlalchemy.org/trac/ticket/1150)
- The echo_uow flag on Session is deprecated, and unit-of-work
  logging is now application-level only, not per-session level.
- Removed conflicting contains() operator from
  InstrumentedAttribute which didn’t accept escape kwaarg.
  References: [#1153](https://www.sqlalchemy.org/trac/ticket/1153)

### sql

- Temporarily rolled back the “ORDER BY” enhancement from.  This feature is on hold pending further
  development.
  References: [#1068](https://www.sqlalchemy.org/trac/ticket/1068)
- The exists() construct won’t “export” its contained list
  of elements as FROM clauses, allowing them to be used more
  effectively in the columns clause of a SELECT.
- and_() and or_() now generate a ColumnElement, allowing
  boolean expressions as result columns, i.e.
  select([and_(1, 0)]).
  References: [#798](https://www.sqlalchemy.org/trac/ticket/798)
- Bind params now subclass ColumnElement which allows them to be
  selectable by orm.query (they already had most ColumnElement
  semantics).
- Added select_from() method to exists() construct, which becomes
  more and more compatible with a regular select().
- Added func.min(), func.max(), func.sum() as “generic functions”,
  which basically allows for their return type to be determined
  automatically.  Helps with dates on SQLite, decimal types,
  others.
  References: [#1160](https://www.sqlalchemy.org/trac/ticket/1160)
- added decimal.Decimal as an “auto-detect” type; bind parameters
  and generic functions will set their type to Numeric when a
  Decimal is used.

### schema

- Added “sorted_tables” accessor to MetaData, which returns
  Table objects sorted in order of dependency as a list.
  This deprecates the MetaData.table_iterator() method.
  The “reverse=False” keyword argument has also been
  removed from util.sort_tables(); use the Python
  ‘reversed’ function to reverse the results.
  References: [#1033](https://www.sqlalchemy.org/trac/ticket/1033)
- The ‘length’ argument to all Numeric types has been renamed
  to ‘scale’.  ‘length’ is deprecated and is still accepted
  with a warning.
- Dropped 0.3-compatibility for user defined types
  (convert_result_value, convert_bind_param).

### mysql

- The ‘length’ argument to MSInteger, MSBigInteger, MSTinyInteger,
  MSSmallInteger and MSYear has been renamed to ‘display_width’.
- Added MSMediumInteger type.
  References: [#1146](https://www.sqlalchemy.org/trac/ticket/1146)
- the function func.utc_timestamp() compiles to UTC_TIMESTAMP, without
  the parenthesis, which seem to get in the way when using in
  conjunction with executemany().

### oracle

- limit/offset no longer uses ROW NUMBER OVER to limit rows,
  and instead uses subqueries in conjunction with a special
  Oracle optimization comment.  Allows LIMIT/OFFSET to work
  in conjunction with DISTINCT.
  References: [#536](https://www.sqlalchemy.org/trac/ticket/536)
- has_sequence() now takes the current “schema” argument into
  account
  References: [#1155](https://www.sqlalchemy.org/trac/ticket/1155)
- added BFILE to reflected type names
  References: [#1121](https://www.sqlalchemy.org/trac/ticket/1121)

### misc

- Fixed bug whereby mapper couldn’t initialize if a composite
  primary key referenced another table that was not defined
  yet.
  References: [#1161](https://www.sqlalchemy.org/trac/ticket/1161)
- Fixed exception throw which would occur when string-based
  primaryjoin condition was used in conjunction with backref.

## 0.5.0beta3

Released: Mon Aug 04 2008

### orm

- The “entity_name” feature of SQLAlchemy mappers has been
  removed.  For rationale, see [https://tinyurl.com/6nm2ne](https://tinyurl.com/6nm2ne)
- the “autoexpire” flag on Session, sessionmaker(), and
  scoped_session() has been renamed to “expire_on_commit”.  It
  does not affect the expiration behavior of rollback().
- fixed endless loop bug which could occur within a mapper’s
  deferred load of inherited attributes.
- a legacy-support flag “_enable_transaction_accounting” flag
  added to Session which when False, disables all
  transaction-level object accounting, including expire on
  rollback, expire on commit, new/deleted list maintenance, and
  autoflush on begin.
- The ‘cascade’ parameter to relation() accepts None as a value,
  which is equivalent to no cascades.
- A critical fix to dynamic relations allows the “modified”
  history to be properly cleared after a flush().
- user-defined @properties on a class are detected and left in
  place during mapper initialization.  This means that a
  table-bound column of the same name will not be mapped at all
  if a @property is in the way (and the column is not remapped
  to a different name), nor will an instrumented attribute from
  an inherited class be applied.  The same rules apply for names
  excluded using the include_properties/exclude_properties
  collections.
- Added a new SessionExtension hook called after_attach().  This
  is called at the point of attachment for objects via add(),
  add_all(), delete(), and merge().
- A mapper which inherits from another, when inheriting the
  columns of its inherited mapper, will use any reassigned
  property names specified in that inheriting mapper.
  Previously, if “Base” had reassigned “base_id” to the name
  “id”, “SubBase(Base)” would still get an attribute called
  “base_id”.  This could be worked around by explicitly stating
  the column in each submapper as well but this is fairly
  unworkable and also impossible when using declarative.
  References: [#1111](https://www.sqlalchemy.org/trac/ticket/1111)
- Fixed a series of potential race conditions in Session whereby
  asynchronous GC could remove unmodified, no longer referenced
  items from the session as they were present in a list of items
  to be processed, typically during session.expunge_all() and
  dependent methods.
- Some improvements to the _CompileOnAttr mechanism which should
  reduce the probability of “Attribute x was not replaced during
  compile” warnings. (this generally applies to SQLA hackers,
  like Elixir devs).
- Fixed bug whereby the “unsaved, pending instance” FlushError
  raised for a pending orphan would not take superclass mappers
  into account when generating the list of relations responsible
  for the error.

### sql

- func.count() with no arguments renders as COUNT(*), equivalent
  to func.count(text(‘*’)).
- simple label names in ORDER BY expressions render as
  themselves, and not as a re-statement of their corresponding
  expression.  This feature is currently enabled only for
  SQLite, MySQL, and PostgreSQL.  It can be enabled on other
  dialects as each is shown to support this
  behavior.
  References: [#1068](https://www.sqlalchemy.org/trac/ticket/1068)

### mysql

- Quoting of MSEnum values for use in CREATE TABLE is now
  optional & will be quoted on demand as required.  (Quoting was
  always optional for use with existing tables.)
  References: [#1110](https://www.sqlalchemy.org/trac/ticket/1110)

### misc

- Class-bound attributes sent as arguments to relation()’s
  remote_side and foreign_keys parameters are now accepted,
  allowing them to be used with declarative.  Additionally fixed
  bugs involving order_by being specified as a class-bound
  attribute in conjunction with eager loading.
- declarative initialization of Columns adjusted so that
  non-renamed columns initialize in the same way as a non
  declarative mapper.  This allows an inheriting mapper to set
  up its same-named “id” columns in particular such that the
  parent “id” column is favored over the child column, reducing
  database round trips when this value is requested.

## 0.5.0beta2

Released: Mon Jul 14 2008

### orm

- In addition to expired attributes, deferred attributes also
  load if their data is present in the result set.
  References: [#870](https://www.sqlalchemy.org/trac/ticket/870)
- session.refresh() raises an informative error message if the
  list of attributes does not include any column-based
  attributes.
- query() raises an informative error message if no columns or
  mappers are specified.
- lazy loaders now trigger autoflush before proceeding.  This
  allows expire() of a collection or scalar relation to function
  properly in the context of autoflush.
- column_property() attributes which represent SQL expressions
  or columns that are not present in the mapped tables (such as
  those from views) are automatically expired after an INSERT or
  UPDATE, assuming they have not been locally modified, so that
  they are refreshed with the most recent data upon access.
  References: [#887](https://www.sqlalchemy.org/trac/ticket/887)
- Fixed explicit, self-referential joins between two
  joined-table inheritance mappers when using query.join(cls,
  aliased=True).
  References: [#1082](https://www.sqlalchemy.org/trac/ticket/1082)
- Fixed query.join() when used in conjunction with a
  columns-only clause and a SQL-expression ON clause in the
  join.
- The “allow_column_override” flag from mapper() has been
  removed.  This flag is virtually always misunderstood.  Its
  specific functionality is available via the
  include_properties/exclude_properties mapper arguments.
- Repaired __str__() method on Query.
  References: [#1066](https://www.sqlalchemy.org/trac/ticket/1066)
- Session.bind gets used as a default even when table/mapper
  specific binds are defined.

### sql

- Added new match() operator that performs a full-text search.
  Supported on PostgreSQL, SQLite, MySQL, MS-SQL, and Oracle
  backends.

### schema

- Added prefixes option to Table that accepts a list of
  strings to insert after CREATE in the CREATE TABLE statement.
  References: [#1075](https://www.sqlalchemy.org/trac/ticket/1075)
- Unicode, UnicodeText types now set “assert_unicode” and
  “convert_unicode” by default, but accept overriding
  **kwargs for these values.

### extensions

- Declarative supports a __table_args__ class variable, which is
  either a dictionary, or tuple of the form (arg1, arg2, …,
  {kwarg1:value, …}) which contains positional + kw arguments
  to be passed to the Table constructor.
  References: [#1096](https://www.sqlalchemy.org/trac/ticket/1096)

### sqlite

- Modified SQLite’s representation of “microseconds” to match
  the output of str(somedatetime), i.e. in that the microseconds
  are represented as fractional seconds in string format.  This
  makes SQLA’s SQLite date type compatible with datetimes that
  were saved directly using Pysqlite (which just calls str()).
  Note that this is incompatible with the existing microseconds
  values in a SQLA 0.4 generated SQLite database file.
  To get the old behavior globally:
  > from sqlalchemy.databases.sqlite import DateTimeMixin
  > DateTimeMixin.__legacy_microseconds__ = True
  To get the behavior on individual DateTime types:
  > t = sqlite.SLDateTime()
  > t.__legacy_microseconds__ = True
  Then use “t” as the type on the Column.
  References: [#1090](https://www.sqlalchemy.org/trac/ticket/1090)
- SQLite Date, DateTime, and Time types only accept Python
  datetime objects now, not strings.  If you’d like to format
  dates as strings yourself with SQLite, use a String type.  If
  you’d like them to return datetime objects anyway despite
  their accepting strings as input, make a TypeDecorator around
  String - SQLA doesn’t encourage this pattern.

## 0.5.0beta1

Released: Thu Jun 12 2008

### general

- global “propagate”->”propagate” change.

### orm

- polymorphic_union() function respects the “key” of each
  Column if they differ from the column’s name.
- Fixed 0.4-only bug preventing composite columns
  from working properly with inheriting mappers
  References: [#1199](https://www.sqlalchemy.org/trac/ticket/1199)
- Fixed RLock-related bug in mapper which could deadlock upon
  reentrant mapper compile() calls, something that occurs when
  using declarative constructs inside of ForeignKey objects.
  Ported from 0.5.
- Fixed bug in composite types which prevented a primary-key
  composite type from being mutated.
  References: [#1213](https://www.sqlalchemy.org/trac/ticket/1213)
- Added ScopedSession.is_active accessor.
  References: [#976](https://www.sqlalchemy.org/trac/ticket/976)
- Class-bound accessor can be used as the argument to
  relation() order_by.
  References: [#939](https://www.sqlalchemy.org/trac/ticket/939)
- Fixed shard_id argument on ShardedSession.execute().
  References: [#1072](https://www.sqlalchemy.org/trac/ticket/1072)

### sql

- Connection.invalidate() checks for closed status
  to avoid attribute errors.
  References: [#1246](https://www.sqlalchemy.org/trac/ticket/1246)
- NullPool supports reconnect on failure behavior.
  References: [#1094](https://www.sqlalchemy.org/trac/ticket/1094)
- The per-dialect cache used by TypeEngine to cache
  dialect-specific types is now a WeakKeyDictionary.
  This to prevent dialect objects from
  being referenced forever for an application that
  creates an arbitrarily large number of engines
  or dialects.   There is a small performance penalty
  which will be resolved in 0.6.
  References: [#1299](https://www.sqlalchemy.org/trac/ticket/1299)
- Fixed SQLite reflection methods so that non-present
  cursor.description, which triggers an auto-cursor
  close, will be detected so that no results doesn’t
  fail on recent versions of pysqlite which raise
  an error when fetchone() called with no rows present.

### mysql

- Fixed bug in exception raise when FK columns not present
  during reflection.
  References: [#1241](https://www.sqlalchemy.org/trac/ticket/1241)

### oracle

- Fixed bug which was preventing out params of certain types
  from being received; thanks a ton to huddlej at wwu.edu !
  References: [#1265](https://www.sqlalchemy.org/trac/ticket/1265)

### misc

- The “__init__” trigger/decorator added by mapper now attempts
  to exactly mirror the argument signature of the original
  __init__.  The pass-through for ‘_sa_session’ is no longer
  implicit- you must allow for this keyword argument in your
  constructor.
- ClassState is renamed to ClassManager.
- Classes may supply their own InstrumentationManager by
  providing a __sa_instrumentation_manager__ property.
- Custom instrumentation may use any mechanism to associate a
  ClassManager with a class and an InstanceState with an
  instance.  Attributes on those objects are still the default
  association mechanism used by SQLAlchemy’s native
  instrumentation.
- Moved entity_name, _sa_session_id, and _instance_key from the
  instance object to the instance state.  These values are still
  available in the old way, which is now deprecated, using
  descriptors attached to the class.  A deprecation warning will
  be issued when accessed.
- The _prepare_instrumentation alias for prepare_instrumentation
  has been removed.
- sqlalchemy.exceptions has been renamed to sqlalchemy.exc.  The
  module may be imported under either name.
- ORM-related exceptions are now defined in sqlalchemy.orm.exc.
  ConcurrentModificationError, FlushError, and
  UnmappedColumnError compatibility aliases are installed in
  sqlalchemy.exc during the import of sqlalchemy.orm.
- sqlalchemy.logging has been renamed to sqlalchemy.log.
- The transitional sqlalchemy.log.SADeprecationWarning alias for
  the warning’s definition in sqlalchemy.exc has been removed.
- exc.AssertionError has been removed and usage replaced with
  Python’s built-in AssertionError.
- The behavior of MapperExtensions attached to multiple,
  entity_name= primary mappers for a single class has been
  altered.  The first mapper() defined for a class is the only
  mapper eligible for the MapperExtension ‘instrument_class’,
  ‘init_instance’ and ‘init_failed’ events.  This is backwards
  incompatible; previously the extensions of last mapper defined
  would receive these events.
- Added support for returning values from inserts (2.0+ only),
  updates and deletes (2.1+ only).
- Added Index reflection support to Postgres, using a
  great patch we long neglected, submitted by
  Ken Kuhlman.
  References: [#714](https://www.sqlalchemy.org/trac/ticket/714)
