How to fix P3001: Migration possible with destructive changes and possible data loss in Prisma

Run npx prisma migrate dev to see the detailed warning message. Prisma will tell you exactly which change is destructive. For example: "The migration will add a required column status without a default value to the User table which currently has 5 rows."

If you're adding a required field, add a default value in your schema:

model User {
  id    Int     @id @default(autoincrement())
  name  String  @default("Unknown")  // Add @default()
  email String  @unique
}

Then run npx prisma migrate dev --name add_name_field

If you can't provide a sensible default, make the field optional first:

model User {
  id    Int     @id @default(autoincrement())
  name  String?  // Optional with ?
  email String   @unique
}

Run the migration, backfill the data with your application, then make it required in a second migration.

For sophisticated changes (renaming fields, transforming data), create a migration without applying it:

npx prisma migrate dev --name transform_user_status --create-only

This creates the migration file in prisma/migrations/ but doesn't apply it. Edit the SQL file to add your custom data transformation logic, then run npx prisma migrate dev again to apply it.

If you're in development and the data doesn't matter, you can reset:

npx prisma migrate reset

OR accept data loss for a single migration:

npx prisma migrate dev --name my_migration
# When prompted, choose to reset the database

NEVER use these approaches in production.

For production databases:

1. Deploy migration 1: Add new nullable column

newStatus String?

2. Deploy your application code to backfill the column with values

3. Deploy migration 2: Make the column required

newStatus String @default("pending")

4. Remove the old column in a follow-up migration

This prevents data loss and allows rollback at each step.

Always review generated migrations before applying them:

cat prisma/migrations/*/migration.sql

Ensure it matches your expectations. If Prisma generated incorrect SQL (rare), edit the migration file before applying it. For detailed info, see the Prisma Migrate customization guide.