Adding Prisma Migrate to an existing project

Introspect to create or update your Prisma schema

Make sure your Prisma schema is in sync with your database schema. This should already be true if you are using a previous version of Prisma Migrate.

1. Introspect the database to make sure that your Prisma schema is up-to-date:

   $prisma db pull

Create a baseline migration

Baselining is the process of initializing a migration history for a database that:

• ✔ Existed before you started using Prisma Migrate
• ✔ Contains data that must be maintained (like production), which means that the database cannot be reset

Baselining tells Prisma Migrate to assume that one or more migrations have already been applied. This prevents generated migrations from failing when they try to create tables and fields that already exist.

To create a baseline migration:

1. If you have a prisma/migrations folder, delete, move, rename, or archive this folder.

2. Run the following command to create a migrations directory inside with your preferred name. This example will use 0_init for the migration name:

   $mkdir -p prisma/migrations/0_init

   Then 0_ is important because Prisma Migrate applies migrations in a lexicographic order. You can use a different value such as the current timestamp.

3. Generate a migration and save it to a file using prisma migrate diff

   $npx prisma migrate diff \
   $--from-empty \
   $--to-schema-datamodel prisma/schema.prisma \
   $--script > prisma/migrations/0_init/migration.sql

4. Review the generated migration

Work around features not supported by Prisma Schema Language

To include unsupported database features that already exist in the database, you must replace or modify the initial migration SQL:

1. Open the migration.sql file generated in the Create a baseline migration section.

2. Modify the generated SQL. For example:

   • If the changes are minor, you can append additional custom SQL to the generated migration - the following example creates a partial index:

   /* Generated migration SQL */
   
   CREATE UNIQUE INDEX tests_success_constraint ON posts (subject, target)
    WHERE success;

   • If the changes are significant, it can be easier to replace the entire migration file with the result of a database dump (mysqldump, pg_dump)

Apply the initial migrations

To apply your initial migration(s):

1. Run the following command against your database:

   $npx prisma migrate resolve --applied 0_init

2. Review the database schema to ensure the migration leads to the desired end-state (for example, by comparing the schema to the production database).

The new migration history and the database schema should now be in sync with your Prisma schema.

Commit the migration history and Prisma schema

Commit the following to source control:

• The entire migration history folder
• The schema.prisma file