Prisma 7 Custom Output Migration

Migrate a Prisma 7 project from the deprecated prisma-client-js generator (which outputs to node_modules/.prisma/client/) to the prisma-client generator with a custom output directory. This eliminates an entire class of monorepo bugs caused by stale nested node_modules copies.

Citations:

• Prisma v7 Turborepo guide
• Prisma v7 upgrade guide
• Prisma generators reference

Why This Migration Matters

With prisma-client-js, the generated client lives in node_modules/.prisma/client/. In monorepos, this causes:

1. Hoisting bugs — package managers may create nested node_modules/@prisma/client/ copies in workspace packages that declare @prisma/client as a dependency. prisma generate writes to root, but TypeScript resolves through the nested copy.
2. Stale build caches — CI/CD (especially Vercel) caches node_modules between deploys. After schema changes or Prisma upgrades, the cached nested copies contain stale types.
3. Phantom type errors — Property 'X' does not exist on type 'PrismaClient' when the model IS in the schema.

With prisma-client, the generated client lives in a directory controlled by the project (e.g., packages/db/src/generated/prisma/). No node_modules resolution games.

Detection: Is This Migration Needed?

Check the schema file for the deprecated pattern:

# DEPRECATED — needs migration
generator client {
  provider = "prisma-client-js"
  # no output directive — defaults to node_modules
}

Check for nested .prisma directories:

find packages -path '*/node_modules/.prisma' -type d

If either is true, proceed with migration.

Migration Steps

1. Update Schema Generator

Change the generator block in the schema file (usually prisma/schema.prisma):

generator client {
  provider = "prisma-client"
  output   = "<relative-path-to-output>"
}

The output path is relative to the schema file. Common patterns:

Schema location	DB package location	Output value
prisma/schema.prisma	packages/db/src/	"../packages/db/src/generated/prisma"
packages/db/prisma/schema.prisma	packages/db/src/	"../src/generated/prisma"
schema.prisma (root)	src/	"./src/generated/prisma"

2. Update .gitignore

Add the new generated output directory and remove the old node_modules-based entry:

# Prisma generated client (output of `prisma generate`)
<path-to-generated-dir>

3. Run prisma generate

bunx prisma generate   # or npx/pnpm exec

Verify output appears at the configured path.

4. Update DB Package Imports

Change all imports in the database package from @prisma/client to the generated path:

// Before
import { PrismaClient } from '@prisma/client'
import { Prisma } from '@prisma/client'

// After
import { PrismaClient } from './generated/prisma/client'
import { Prisma } from './generated/prisma/client'

5. Update DB Package Exports

The database package barrel (index.ts) should re-export everything downstream needs:

export { prisma } from './client'
export { Prisma, PrismaClient } from './generated/prisma/client'
export type { YourModel, YourEnum } from './generated/prisma/client'

Re-exporting PrismaClient allows seed files and CLI scripts to construct their own instances when needed.

6. Keep @prisma/client as a Runtime Dependency

Do NOT remove @prisma/client from dependencies. The generated client internally imports @prisma/client/runtime/client for the Prisma runtime engine. What changes is that your code no longer imports PrismaClient or types from @prisma/client — you import from the generated path instead. But the package itself must remain installed.

{
  "dependencies": {
    "@prisma/adapter-pg": "^7.4.0",
    "@prisma/client": "^7.4.0",
    "pg": "^8.17.1"
  }
}

Why it works locally without it: Bun/npm/pnpm hoist @prisma/client to root node_modules (transitively via prisma CLI). But CI's Vite import analysis resolves from the package directory context, where it may not be found if not declared as a direct dependency.

7. Update Seed Files and CLI Scripts

Files that construct their own PrismaClient (seeds, scripts) need updated imports:

// Before
import { PrismaClient } from '@prisma/client'

// After — use relative path to generated dir
import { PrismaClient } from '../../packages/db/src/generated/prisma/client'

// Or import through the DB package (if it re-exports PrismaClient)
import { PrismaClient } from '@baptize/db'

8. Clean Up Postinstall

If the project had workarounds for nested .prisma cleanup, remove them. The postinstall only needs:

"postinstall": "DATABASE_URL=${DATABASE_URL:-placeholder} prisma generate || true"

9. Verify

# Regenerate from scratch
rm -rf <generated-output-dir>
bunx prisma generate

# Type check
bunx tsc --noEmit

# Tests
bunx vitest run

# Confirm no stale imports
grep -rn "from '@prisma/client'" packages/ apps/ src/

Common Pitfalls

Vercel Build Command

Vercel's build command should still run prisma generate — it writes to the source tree, not node_modules, so caching issues are eliminated:

cd ../.. && DATABASE_URL=placeholder bunx prisma generate && bunx turbo build

Driver Adapter Import

@prisma/adapter-pg (and other adapters) remain as regular npm dependencies — only @prisma/client is removed. The adapter is imported normally:

import { PrismaPg } from '@prisma/adapter-pg'

Type Re-exports

When re-exporting model types from the DB package, use export type for types and export for runtime values:

// Runtime values
export { prisma } from './client'
export { Prisma, PrismaClient } from './generated/prisma/client'

// Type-only exports
export type { User, Organization } from './generated/prisma/client'

Workflow Files (Vercel Workflows)

'use step' functions that dynamically import @baptize/db work unchanged — the import resolves through the workspace package, which now internally uses the generated path:

'use step'
const { prisma } = await import('@baptize/db')  // no change needed

Additional Resources

Reference Files

• references/migration-checklist.md — Step-by-step checklist with verification commands
• references/troubleshooting.md — Common errors and fixes during migration

Example Files

• examples/schema-generator.prisma — Correct generator block examples
• examples/db-package-index.ts — Barrel exports from generated path

The singleton client pattern (with lazy proxy and PrismaPg adapter) is documented inline in Step 4 above. The only import change is PrismaClient from the generated path instead of @prisma/client.