Prisma schema design, migrations, client generation and query patterns. Use when changing a Prisma schema, writing a migration, or querying with Prisma Client.
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---
name: prisma-database
description: "Prisma schema design, migrations, client generation and query patterns. Use when changing a Prisma schema, writing a migration, or querying with Prisma Client."
---
# Prisma Database
Project schema and connection details: `.opencastle/stack/database-config.md`. Docs: https://www.prisma.io/docs
## Migration rules
- `npx prisma migrate dev` in development only — **never in production**; it can reset data. CI/production uses `npx prisma migrate deploy`.
- Inspect `prisma/migrations/<timestamp>/migration.sql` before applying. Destructive operations (drops, column rewrites) need an explicit backfill step added to the migration.
- **Never edit an already-applied migration file** — the checksum is recorded and will fail. Write a corrective migration instead.
- `npx prisma generate` after every schema change; a stale client silently mismatches the DB. `npx prisma db push` skips migration history entirely — prototyping only.
## Schema gotchas
- Use `cuid()` / `uuid()` for IDs, not serial increments, in anything distributed.
- Renaming a field without matching `@map`/`@@map` produces a *column drop plus add*, not a rename. Check both when renaming.
- Add `@@index` explicitly on frequently queried columns — the schema does not imply them.
- Write `@relation` explicitly, including `onDelete` (e.g. `onDelete: Cascade`); leaving it implicit means the delete behavior is whatever the connector defaults to.
- Include `createdAt @default(now())` and `updatedAt @updatedAt` for auditability.
## Client and queries
Hot reload in dev creates a new `PrismaClient` per reload and exhausts the connection pool. Use the global singleton:
```typescript
const globalForPrisma = globalThis as unknown as { prisma?: PrismaClient };
export const prisma = globalForPrisma.prisma ?? new PrismaClient();
if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma;
```
Use `select` for narrow reads, `include` for relations, `prisma.$transaction` for multi-step writes. Catch error code **`P2002`** for unique-constraint violations and handle it rather than letting it surface as a 500.
Other commands: `prisma studio` (visual editor), `prisma db pull` (introspect), `prisma db seed`, `prisma validate`, `prisma format`.
