The Prisma Migration That Dropped a Production Column (No Way to Recover)

"Where did the user's phone number go?"

We had a simple schema change: rename phone to phone_number.

I changed the Prisma schema, ran prisma migrate dev, and pushed to production.

But the column wasn't renamed – it was dropped. And all 50,000 phone numbers were gone.

The Setup

Original schema:

model User {
  id    Int    @id @default(autoincrement())
  email String @unique
  phone String  // ← this column
}

I changed it to:

model User {
  id           Int    @id @default(autoincrement())
  email        String @unique
  phone_number String  // ← renamed
}

The Migration

npx prisma migrate dev --name rename_phone_column

Prisma generated this SQL:

-- Prisma generated (WRONG!)
ALTER TABLE "User" DROP COLUMN "phone";
ALTER TABLE "User" ADD COLUMN "phone_number" TEXT;

Instead of RENAME COLUMN, Prisma dropped and recreated the column. All data in phone was lost.

Why? Because Prisma doesn't know you want to rename. It sees a removed field and a new field – and assumes you want to drop+add.

The Fix (Prevention)

You must use @map to tell Prisma the underlying database column name:

model User {
  id           Int    @id @default(autoincrement())
  email        String @unique
  phone_number String @map("phone")  // ← maps to existing column name
}

Then the migration becomes a no‑op (column already exists).

After deploying, you can later remove the @map in a second migration.

The Recovery

We had to restore from a backup taken 6 hours before.

# Restore from AWS RDS snapshot
aws rds restore-db-instance-from-db-snapshot   --db-instance-identifier mydb-restored   --db-snapshot-identifier mydb-snapshot

Then manually export the phone column and join back. Lost 4 hours of new orders.

What I Learned

• Prisma doesn't auto‑detect renames – you must use @map.
• Always check the generated SQL before applying to production.
• Use prisma migrate diff to see what will happen.
• Never trust a migration without a backup.

Now our CI runs prisma migrate diff and fails if it sees DROP COLUMN on non‑nullable fields.