Migration troubleshooting in development

MongoDB not supported
Prisma Migrate does not currently support the MongoDB connector.

This guide describes how to resolve issues with Prisma Migrate in a development environment, which often involves resetting your database. For production-focused troubleshooting, see:

Handling migration history conflicts

A migration history conflict occurs when there are discrepancies between the migrations folder in the file system and the _prisma_migrations table in the database.

Causes of migration history conflict in a development environment

  • A migration that has already been applied is later modified
  • A migration that has already been applied is missing from the file system

In a development environment, switching between feature branches can result in a history conflict because the _prisma_migrations table contains migrations from branch-1, and switching to branch-2 might cause some of those migrations to disappear.

Note: You should never purposefully delete or edit a migration, as this might result in discrepancies between development and production.

Fixing a migration history conflict in a development environment

If Prisma Migrate detects a migration history conflict when you run prisma migrate dev, the CLI will ask to reset the database and reapply the migration history.

Schema drift

Database schema drift occurs when your database schema is out of sync with your migration history - the database schema has 'drifted away' from the source of truth.

Causes of schema drift in a development environment

Schema drift can occur if:

  • The database schema was changed without using migrations - for example, by using prisma db push or manually changing the database schema.

Note: The shadow database is required to detect schema drift, and can therefore only be done in a development environment.

Fixing schema drift in a development environment

If you made manual changes to the database that you do not want to keep, or can easily replicate in the Prisma schema:

  1. Reset your database:

    $npx prisma migrate reset
  2. Replicate the changes in the Prisma schema and generate a new migration:

    $npx prisma migrate dev

If you made manual changes to the database that you want to keep, you can:

  1. Introspect the database:

    $npx prisma db pull

    Prisma will update your schema with the changes made directly in the database.

  2. Generate a new migration to include the introspected changes in your migration history:

    $npx prisma migrate dev --name introspected_change

    Prisma Migrate will prompt you to reset, then applies all existing migrations and a new migration based on the introspected changes. Your database and migration history are now in sync, including your manual changes.

Failed migrations

Causes of failed migrations in a development environment

A migration might fail if:

  • You modify a migration before running it and introduce a syntax error
  • You add a mandatory (NOT NULL) column to a table that already has data
  • The migration process stopped unexpectedly
  • The database shut down in the middle of the migration process

Each migration in the _prisma_migrations table has a logs column that stores the error.

Fixing failed migrations in a development environment

The easiest way to handle a failed migration in a developer environment is to address the root cause and reset the database. For example:

  • If you introduced a SQL syntax error by manually editing the database, update the migration.sql file that failed and reset the database:

    $prisma migrate reset
  • If you introduced a change in the Prisma schema that cannot be applied to a database with data (for example, a mandatory column in a table with data):

    1. Delete the migration.sql file.

    2. Modify the schema - for example, add a default value to the mandatory field.

    3. Migrate:

      $prisma migrate dev

      Prisma Migrate will prompt you to reset the database and re-apply all migrations.

  • If something interrupted the migration process, reset the database:

    $prisma migrate reset

Prisma Migrate and PgBouncer

You might see the following error if you attempt to run Prisma Migrate commands in an environment that uses PgBouncer for connection pooling:

Error: undefined: Database error
Error querying the database: db error: ERROR: prepared statement "s0" already exists

See Prisma Migrate and PgBouncer workaround for further information and a workaround. Follow GitHub issue #6485 for updates.

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