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15.5 Prisma Migrations — Schema Management and Seeding

Migration Workflow​

Development flow:
  1. Modify schema.prisma
  2. npx prisma migrate dev  → Create migration file + apply to DB
  3. npx prisma generate     → Regenerate Prisma Client (automatic)
  4. Commit migration files to git

Deployment flow:
  1. git pull (with migration files)
  2. npx prisma migrate deploy  → Apply only unapplied migrations in order

Migration Commands​

# Development — create and apply migration
npx prisma migrate dev --name add-user-avatar

# Check migration history
npx prisma migrate status

# Production deployment (use in CI/CD)
npx prisma migrate deploy

# Reset dev DB (re-runs all migrations from scratch)
npx prisma migrate reset

# Rollback specific migration (not supported — requires manual SQL)

Example Generated Migration File​

-- prisma/migrations/20240115000000_add_user_avatar/migration.sql

-- AlterTable
ALTER TABLE "User" ADD COLUMN "avatar" TEXT;
ALTER TABLE "User" ADD COLUMN "avatarUpdatedAt" TIMESTAMP(3);

Schema Change Patterns​

Add Column (Safe)​

model User {
  // Existing fields...
  avatar    String?  // Nullable — no impact on existing data
  bio       String   @default("")  // Set default value
}

Rename Column​

model User {
  // Rename firstName → name
  // Direct rename causes data loss! Use @map
  name String @map("firstName")  // Keep DB column name, change Prisma accessor
}

Delete Column (Caution)​

// Step 1: Remove references to the field in application code
// Step 2: Make nullable and deploy
// Step 3: Run actual column drop migration

Rename Table​

model Article {
  @@map("Post")  // DB table name is "Post", Prisma model name is "Article"
}

Data Seeding​

// prisma/seed.ts
import { PrismaClient } from '@prisma/client'
import * as bcrypt from 'bcrypt'

const prisma = new PrismaClient()

async function main() {
  // Clean up existing data (optional)
  await prisma.post.deleteMany()
  await prisma.user.deleteMany()

  // Create admin account
  const admin = await prisma.user.create({
    data: {
      email: 'admin@example.com',
      name: 'Admin',
      password: await bcrypt.hash('adminpassword', 10),
      role: 'ADMIN',
    },
  })

  // Create regular users with posts
  const users = await Promise.all(
    Array.from({ length: 5 }, (_, i) =>
      prisma.user.create({
        data: {
          email: `user${i + 1}@example.com`,
          name: `User ${i + 1}`,
          password: await bcrypt.hash('password', 10),
          posts: {
            create: Array.from({ length: 3 }, (_, j) => ({
              title: `User ${i + 1} Post ${j + 1}`,
              content: `Content ${j + 1}`,
              published: j < 2,  // First 2 posts published
            })),
          },
        },
      })
    )
  )

  console.log(`Created ${users.length} users`)
}

main()
  .catch(console.error)
  .finally(async () => {
    await prisma.$disconnect()
  })

Configure Seed in package.json​

{
  "prisma": {
    "seed": "tsx prisma/seed.ts"
  },
  "devDependencies": {
    "tsx": "^4.0.0"
  }
}
# Run seed
npx prisma db seed

# Reset migrations + auto-run seed
npx prisma migrate reset

Per-Environment Database Configuration​

# .env (development)
DATABASE_URL="postgresql://user:password@localhost:5432/myapp_dev"

# .env.test (test environment)
DATABASE_URL="postgresql://user:password@localhost:5432/myapp_test"

# .env.production (production)
DATABASE_URL="postgresql://user:password@prod-db:5432/myapp_prod?connection_limit=10&pool_timeout=20"

Pro Tips​

Schema Validation and Formatting

# Validate schema syntax
npx prisma validate

# Format schema file
npx prisma format

# Generate ERD diagram (requires prisma-erd-generator)
npx prisma generate  # Auto-generates ERD.svg

CI/CD Pipeline Configuration

# .github/workflows/deploy.yml
jobs:
  deploy:
    steps:
      - name: Apply migrations
        run: npx prisma migrate deploy
        env:
          DATABASE_URL: ${{ secrets.DATABASE_URL }}

      - name: Generate Prisma Client
        run: npx prisma generate

Split Prisma Schema (Large Projects)

// prisma/schema.prisma
generator client {
  provider        = "prisma-client-js"
  previewFeatures = ["prismaSchemaFolder"]
}

// prisma/schema/user.prisma — Split models into separate files (Preview feature)
model User {
  id    Int    @id
  email String @unique
}
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