Agent Skills: Prisma Patterns

Prisma Patterns

Production patterns and non-obvious traps for Prisma ORM in TypeScript backends.

Check your version before applying patterns. The Prisma API surface has evolved across major releases:

npx prisma --version

Notable API differences across versions:

• relationJoins can load relations via JOIN rather than separate queries, but may cause row explosion on large 1:N relations or deep include — benchmark both approaches
• omit field modifier and prisma.$extends Client Extensions API were added
• Newer installs: the package may be named prisma instead of @prisma/client; PrismaClient may require a driver adapter (e.g. @prisma/adapter-pg); datasource.url may live in prisma.config.ts instead of schema.prisma
• CLI commands (migrate dev, migrate deploy, generate) are unchanged across versions

When to Activate

• Designing or modifying Prisma schema models and relations
• Writing queries, transactions, or pagination logic
• Using updateMany, deleteMany, or any bulk operation
• Running or planning database migrations
• Deploying to serverless environments (Vercel, Lambda, Cloudflare Workers)
• Implementing soft delete or multi-tenant row filtering

Core Concepts

ID Strategy

| Strategy | Use When | Avoid When | |---|---|---| | @default(cuid()) | Default choice — URL-safe, sortable, no collisions | Sequential IDs needed for external systems | | @default(uuid()) | Interoperability with non-Prisma systems required | High-write tables (random UUIDs fragment B-tree indexes) | | @default(autoincrement()) | Internal join tables, audit logs | Public-facing IDs (exposes record count) |

Schema Defaults

model User {
  id        String    @id @default(cuid())
  email     String    @unique  // @unique already creates an index — no @@index needed
  name      String
  role      Role      @default(USER)
  posts     Post[]
  createdAt DateTime  @default(now())
  updatedAt DateTime  @updatedAt
  deletedAt DateTime?

  @@index([createdAt])
  @@index([deletedAt, createdAt]) // composite for soft-delete + sort queries
}

• Add @@index on every foreign key and column used in WHERE or ORDER BY.
• Declare deletedAt DateTime? upfront when soft delete is a foreseeable requirement — adding it later requires a migration on a live table.
• updatedAt @updatedAt is set automatically by Prisma on update and upsert only (see Anti-Patterns for bulk update trap).

include vs select

| | include | select | |---|---|---| | Returns | All scalar fields + specified relations | Only specified fields | | Use when | You need most fields plus a relation | Hot paths, large tables, avoiding over-fetch | | Performance | May over-fetch on wide tables | Minimal payload, faster on large datasets | | Prisma 5 note | Uses JOIN by default (relationJoins) | Same |

// include — all columns + relation
const user = await prisma.user.findUnique({
  where: { id },
  include: { posts: { select: { id: true, title: true } } },
});

// select — explicit allowlist
const user = await prisma.user.findUnique({
  where: { id },
  select: { id: true, email: true, name: true },
});

Never return raw Prisma entities from API responses — map to response DTOs to control exposed fields:

// BAD: leaks passwordHash, deletedAt, internal fields
return await prisma.user.findUniqueOrThrow({ where: { id } });

// GOOD: explicit DTO mapping
const user = await prisma.user.findUniqueOrThrow({ where: { id } });
return { id: user.id, name: user.name, email: user.email };

Transaction Form Selection

| Situation | Use | |---|---| | Independent operations, no inter-dependency | Array form | | Later step depends on earlier result | Interactive form | | External calls (email, HTTP) involved | Outside transaction entirely |

// Array form — batched in one round trip
const [user, post] = await prisma.$transaction([
  prisma.user.update({ where: { id }, data: { name } }),
  prisma.post.create({ data: { title, authorId: id } }),
]);

// Interactive form — use tx client only, never the outer prisma client
const post = await prisma.$transaction(async (tx) => {
  const user = await tx.user.findUniqueOrThrow({ where: { id } });
  if (user.role !== 'ADMIN') throw new Error('Forbidden');
  return tx.post.create({ data: { title, authorId: user.id } });
});

PrismaClient Singleton

Each PrismaClient instance opens its own connection pool. Instantiate once.

// lib/prisma.ts

// Option A — adapter-based initialization (required by newer Prisma installs)
import { PrismaClient } from '@prisma/client'; // or the generated client path for your setup
import { PrismaPg } from '@prisma/adapter-pg';

function createPrismaClient() {
  const adapter = new PrismaPg({
    connectionString: process.env.DATABASE_URL!,
  });
  return new PrismaClient({
    adapter,
    log: process.env.NODE_ENV === 'development' ? ['query', 'error'] : ['error'],
  });
}

const globalForPrisma = globalThis as unknown as { prisma?: PrismaClient };

export const prisma = globalForPrisma.prisma ?? createPrismaClient();

if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma;

// Option B — direct initialization (older installs, no adapter needed)
// import { PrismaClient } from '@prisma/client';
// export const prisma = globalForPrisma.prisma ?? new PrismaClient({ ... });

Use Option A if your Prisma install requires an adapter argument in the PrismaClient constructor. Use Option B if new PrismaClient() works without arguments. Let the compiler tell you which is correct.

The globalThis pattern prevents duplicate instances during hot reload (Next.js, nodemon, ts-node-dev).

N+1 Problem

Loading relations inside a loop issues one query per row.

// BAD: N+1 — one extra query per user
const users = await prisma.user.findMany();
for (const user of users) {
  const posts = await prisma.post.findMany({ where: { authorId: user.id } });
}

// GOOD: single query
const users = await prisma.user.findMany({ include: { posts: true } });

With Prisma 5+ relationJoins, the include form uses a single JOIN. On large 1:N sets this may increase result set size — benchmark both approaches if the relation can return many rows per parent.

Code Examples

Cursor Pagination (preferred for feeds and large datasets)

async function getPosts(cursor?: string, limit = 20) {
  const items = await prisma.post.findMany({
    where: { published: true },
    orderBy: [
      { createdAt: 'desc' },
      { id: 'desc' }, // secondary sort prevents unstable pagination on duplicate timestamps
    ],
    take: limit + 1,
    ...(cursor && { cursor: { id: cursor }, skip: 1 }),
  });

  const hasNextPage = items.length > limit;
  if (hasNextPage) items.pop();

  return { items, nextCursor: hasNextPage ? items[items.length - 1].id : null };
}

Fetch limit + 1 and pop — canonical way to detect hasNextPage without an extra count query. Always include a unique field (e.g. id) as a secondary orderBy to prevent unstable pagination when multiple rows share the same timestamp. Use offset pagination only when users need to jump to arbitrary pages (admin tables).

Soft Delete

// Always filter explicitly — do not rely on middleware (hides behavior, hard to debug)
const activeUsers = await prisma.user.findMany({ where: { deletedAt: null } });

await prisma.user.update({ where: { id }, data: { deletedAt: new Date() } });
await prisma.user.update({ where: { id }, data: { deletedAt: null } }); // restore

Error Handling

import { Prisma } from '@prisma/client'; // or the generated client path for your setup

try {
  await prisma.user.create({ data: { email } });
} catch (e) {
  if (e instanceof Prisma.PrismaClientKnownRequestError) {
    if (e.code === 'P2002') throw new ConflictError('Email already exists');
    if (e.code === 'P2025') throw new NotFoundError('Record not found');
    if (e.code === 'P2003') throw new BadRequestError('Referenced record does not exist');
  }
  throw e;
}

Common codes: P2002 unique violation · P2025 not found · P2003 foreign key violation.

Catch at the service boundary and translate to domain errors. Never expose raw Prisma messages to API consumers.

Connection Pool — Serverless

Embed connection params directly in DATABASE_URL — string concatenation breaks if the URL already has query parameters (e.g. ?schema=public):

# .env — preferred: embed params in the URL
DATABASE_URL="postgresql://user:pass@host/db?connection_limit=1&pool_timeout=20"

# With an external pooler (PgBouncer, Supabase pooler)
DATABASE_URL="postgresql://user:pass@host/db?pgbouncer=true&connection_limit=1"

// Vercel, AWS Lambda, and similar serverless runtimes:
// cap pool to 1 per instance; connection_limit and pool_timeout controlled via DATABASE_URL

// Adapter-based setup (if your Prisma install requires an adapter):
import { PrismaClient } from '@prisma/client';
import { PrismaPg } from '@prisma/adapter-pg';

const prisma = new PrismaClient({
  adapter: new PrismaPg({ connectionString: process.env.DATABASE_URL }),
});

// Direct setup (if your Prisma install does not require an adapter):
// const prisma = new PrismaClient();

Anti-Patterns

updateMany returns a count, not records

// BAD: result is { count: 2 } — users[0] is undefined
const users = await prisma.user.updateMany({ where: { role: 'GUEST' }, data: { role: 'USER' } });

// GOOD: capture IDs first, then update, then fetch only the affected rows
const targets = await prisma.user.findMany({
  where: { role: 'GUEST' },
  select: { id: true },
});
const ids = targets.map((u) => u.id);
await prisma.user.updateMany({ where: { id: { in: ids } }, data: { role: 'USER' } });
const updated = await prisma.user.findMany({ where: { id: { in: ids } } });

Same applies to deleteMany — returns { count: n }, never the deleted rows.

$transaction interactive form times out after 5 seconds

// BAD: external call inside transaction exceeds 5s default → "Transaction already closed"
await prisma.$transaction(async (tx) => {
  const user = await tx.user.findUniqueOrThrow({ where: { id } });
  await sendWelcomeEmail(user.email); // external call
  await tx.user.update({ where: { id }, data: { emailSent: true } });
});

// GOOD: external calls outside the transaction
const user = await prisma.user.findUniqueOrThrow({ where: { id } });
await sendWelcomeEmail(user.email);
await prisma.user.update({ where: { id }, data: { emailSent: true } });

// Only raise timeout when bulk processing genuinely needs it
await prisma.$transaction(async (tx) => { ... }, { timeout: 30_000 });

migrate dev can reset the database

migrate dev detects schema drift and may prompt to reset the DB, dropping all data.

# NEVER on shared dev, staging, or production
npx prisma migrate dev --name add_column

# Safe everywhere except local solo dev
npx prisma migrate deploy

# Check drift without applying
npx prisma migrate diff \
  --from-migrations ./prisma/migrations \
  --to-schema-datamodel ./prisma/schema.prisma \
  --shadow-database-url "$SHADOW_DATABASE_URL"

Manually editing a migration file breaks future deploys

Prisma checksums every migration file. Editing after apply causes P3006 checksum mismatch on every environment where the original already ran. Create a new migration instead.

Breaking schema changes require multi-step migration

Adding NOT NULL to an existing column or renaming a column in one migration will lock the table or drop data. Use expand-and-contract:

# Step 1: create migration locally, then deploy
npx prisma migrate dev --name add_new_column   # local only
npx prisma migrate deploy                       # staging / production

// Step 2: backfill data (run in a script or migration job, not in the shell)
await prisma.user.updateMany({ data: { newColumn: derivedValue } });

# Step 3: create the NOT NULL constraint migration locally, then deploy
npx prisma migrate dev --name make_new_column_required  # local only
npx prisma migrate deploy                               # staging / production

@updatedAt does not fire on updateMany

@updatedAt is set automatically only on update and upsert. Bulk writes leave it stale.

// BAD: updatedAt stays at its old value
await prisma.post.updateMany({ where: { authorId }, data: { published: true } });

// GOOD
await prisma.post.updateMany({
  where: { authorId },
  data: { published: true, updatedAt: new Date() },
});

Soft delete + findUniqueOrThrow leaks deleted records

findUniqueOrThrow throws P2025 only when the row does not exist in the DB. Soft-deleted rows still exist and are returned without error.

findUniqueOrThrow requires a unique constraint field in where — adding deletedAt: null alongside id breaks the type because { id, deletedAt } is not a compound unique constraint. Use findFirstOrThrow instead.

// BAD: returns soft-deleted user
const user = await prisma.user.findUniqueOrThrow({ where: { id } });

// BAD: Prisma type error — { id, deletedAt } is not a unique constraint
const user = await prisma.user.findUniqueOrThrow({ where: { id, deletedAt: null } });

// GOOD: findFirstOrThrow supports arbitrary where conditions
const user = await prisma.user.findFirstOrThrow({ where: { id, deletedAt: null } });

deleteMany without where deletes every row

// BAD: silently wipes the table
await prisma.post.deleteMany();

// GOOD
await prisma.post.deleteMany({ where: { authorId: userId } });

Best Practices

| Rule | Reason | |---|---| | migrate deploy in CI/CD, migrate dev only locally | migrate dev can reset the DB on drift | | Map entities to response DTOs | Prevents leaking internal fields | | Catch PrismaClientKnownRequestError at service boundary | Translate to domain errors | | Prefer *OrThrow methods over manual null checks | Throws P2025 automatically; use findFirstOrThrow when filtering non-unique fields | | connection_limit=1 + external pooler in serverless | Prevents connection exhaustion | | Always provide where on deleteMany | Prevents accidental table wipe | | Set updatedAt: new Date() manually in updateMany | @updatedAt skips bulk writes |

Related Skills

• nestjs-patterns — NestJS service layer that integrates Prisma
• postgres-patterns — PostgreSQL-level indexing and connection tuning
• database-migrations — multi-step migration planning for production
• backend-patterns — general API and service layer design