Agent Skills: Generate DocType Controller

Generate DocType Controller

Create document controller classes with lifecycle methods following Frappe patterns.

When to Use

• Need business logic for DocType
• Want lifecycle hooks (validate, before_insert, etc.)
• Prefer class-based controllers
• Need reusable methods

Core Patterns

1. Controller Structure

from frappe_microservice.controller import DocumentController
import frappe

class SalesOrder(DocumentController):
    def validate(self):
        if not self.customer:
            self.throw("Customer is required")
        self.calculate_total()
    
    def before_insert(self):
        if not self.status:
            self.status = 'Draft'
        if not self.transaction_date:
            self.transaction_date = frappe.utils.today()
    
    def after_insert(self):
        self.send_order_notification()
    
    def calculate_total(self):
        self.grand_total = sum(item.amount for item in self.items) if self.items else 0

2. Register Controller

from frappe_microservice.controller import setup_controllers

app = create_microservice("my-service")
setup_controllers(app, controllers_directory="./controllers")

3. Lifecycle Methods

Available: before_validate, validate, before_insert, after_insert, before_update, after_update, before_save, after_save, before_delete, on_trash, on_cancel, on_submit

4. Helper Methods

• self.throw(message) - Raise validation error
• self.get(field, default=None) - Get field value
• self.set(field, value) - Set field value
• self.has_value_changed(fieldname) - Check if changed
• self.get_value_before_save(fieldname) - Get old value

Key Patterns

1. Validation: Use validate() for business rules
2. Defaults: Set in before_insert()
3. Notifications: Send in after_insert() or after_update()
4. Calculations: Create reusable methods
5. Error Handling: Use self.throw() for validation errors

File Naming

• File: sales_order.py → Class: SalesOrder → DocType: Sales Order

Remember: This skill is model-invoked. Claude will use it autonomously when detecting controller development needs.

Decision Tree & Reference

The following material is from Frappe / ERPNext controller skills (frappe-syntax-controllers, frappe-impl-controllers). Use it when mapping lifecycle behavior or aligning with upstream Frappe patterns. Hook names in this microservice controller may differ slightly from core Frappe (e.g. on_update vs after_update); treat the semantics the same unless your SDK docs say otherwise.

Hook selection (what do you need?)

What do you need to do?
|
+-- Validate data or calculate fields?
|   +-- validate (changes to self ARE saved)
|
+-- Action AFTER save (emails, sync, linked docs)?
|   +-- on_update (changes to self are NOT saved — use db_set / set_value)
|
+-- Only for NEW documents?
|   +-- after_insert (runs once on first save only)
|
+-- Custom document name?
|   +-- autoname (set self.name)
|
+-- Before/after SUBMIT?
|   +-- Validate before submit? -> before_submit
|   +-- Create entries after submit? -> on_submit
|
+-- Before/after CANCEL?
|   +-- Check linked docs? -> before_cancel
|   +-- Reverse entries? -> on_cancel
|
+-- Cleanup before delete?
|   +-- on_trash
|
+-- React to ANY value change (including db_set)?
|   +-- on_change (MUST be idempotent)

Quick reference — class, file, and key methods (Frappe)

| Item | Convention | |------|------------| | DocType name | Title Case (e.g. Sales Order) | | Class name | PascalCase (e.g. SalesOrder) | | File path (typical app) | module/doctype/sales_order/sales_order.py | | Base class | from frappe.model.document import Document |

| Method | Role | |--------|------| | autoname() | Custom naming — set self.name | | validate() | Main validation — runs on every save; field changes on self persist | | on_update() | After DB write — assignments to self do not persist without db_set | | on_submit() / on_cancel() | Submittable workflow — implement as a matched pair | | @frappe.whitelist() | Expose method to Desk client (frm.call(...)) |

validate vs on_update

| Aspect | validate | on_update | |--------|------------|-------------| | When | Before DB write | After DB write | | self.x = y persisted? | Yes | No — use db_set or frappe.db.set_value | | Abort save with throw? | Yes | Too late — document already saved |

• NEVER put blocking validation-only logic in on_update — use validate() (or before_submit / similar as appropriate).

Lifecycle execution order (Frappe)

INSERT (new document)

before_insert -> before_naming -> autoname -> before_validate -> validate
-> before_save -> [db_insert] -> after_insert -> on_update -> on_change

SAVE (existing document)

before_validate -> validate -> before_save -> [db_update]
-> on_update -> on_change

SUBMIT (docstatus 0 -> 1)

before_validate -> validate -> before_submit -> [db_update]
-> on_submit -> on_update -> on_change

CANCEL (docstatus 1 -> 2)

before_cancel -> [db_update] -> on_cancel -> on_change

UPDATE AFTER SUBMIT

before_update_after_submit -> [db_update]
-> on_update_after_submit -> on_change

DELETE

on_trash -> [db_delete] -> after_delete

DISCARD [v15+]

before_discard -> [db_set docstatus=2] -> on_discard

Critical rules — ALWAYS / NEVER

1. After on_update: direct self.field = value is not persisted — use self.db_set(...) or frappe.db.set_value(...).
2. NEVER call frappe.db.commit() inside controllers — Frappe commits at end of request; manual commit risks partial updates.
3. ALWAYS call super().validate() (and equivalents) when overriding hooks so base/ERPNext logic still runs unless you intentionally replace it.
4. ALWAYS use self.flags (or equivalent) for data passed between hooks in one transaction — avoid global/external mutable state for this.
5. NEVER duplicate “must-block-save” validation in on_update — validate in validate() / before_submit as applicable.
6. Submittable documents: ALWAYS implement on_submit and on_cancel together — ALWAYS reverse on_submit side effects in on_cancel.

Controller vs Server Script (Frappe apps)

NEED full Python (imports, classes, libs)?           -> Controller
NEED ERPNext/custom app extension / background jobs? -> Controller
Quick validation without a custom app?               -> Server Script (where enabled)

Anti-pattern quick check

| Do NOT | Do instead | |--------|------------| | Expect self.x = y in on_update to save | db_set / frappe.db.set_value | | self.save() recursively from on_update | Risks loops; use db_set or enqueue work | | frappe.db.commit() in controllers | Let the framework manage the transaction | | Heavy work blocking in validate | Consider frappe.enqueue() from on_update | | Skip super() in overrides | Call parent hooks first unless fully replacing behavior | | frappe.get_doc() in hot loops | Prefer frappe.get_cached_doc() when applicable |