Datamodel & Migrations

Introspection (PostgreSQL)


When connecting Prisma to an existing database that already has a database schema and/or contains some data, it can be tedious to manually write the datamodel from scratch while ensuring it matches the structure of the already existing data.

To automate this process, you can use the prisma1 introspect command from the Prisma CLI to generate the datamodel based on the actual structure of the existing data.

The generated SDL serves as a foundation for your Prisma API, but you can easily make modifications afterwards as you see fit. Some common modifications include hiding a table from the Prisma API or renaming a column to a different name.

Introspecting a PostgreSQL database

PostgreSQL uses the following model to organize databases internally:

IMPORTANT: When introspecting a PostgreSQL database, you're actually introspecting a schema and not a database according to the illustrated model. Learn more here.

There are two ways you can use the CLI to introspect a PostgreSQL schema:

  • Using the interactive prisma1 init wizard
  • Using the dedicated prisma1 introspect command

In both cases, you need to provide the connection details for the running PostgreSQL database. This includes the following:

  • Host: The host of your PostgreSQL server, e.g. localhost.
  • Port: The port where your PostgreSQL server listens, e.g. 5432.
  • User & Password: The credentials for your PostgreSQL server.
  • Name of existing database: The name of the PostgreSQL database (according to the illustrated model from above).
  • Use SSL (Yes/No): If your database connection is using SSL, you need to select Yes, otherwise No.
  • Name of existing schema: The name of the PostgreSQL schema (according to the illustrated model from above), e.g. public.

Using the prisma1 init wizard

During the interactive prisma1 init flow you can choose to connect to an existing database with data. The CLI will ask for database connection details (as mentioned above) and verify that it can establish a successfully connection.

If the connection details are valid, the CLI will introspect the database and show you a summary.

When prisma1 init terminates, the CLI has created the following files for you which you can now use to deploy a new Prisma service:

  • datamodel.prisma: Contains the datamodel (in SDL) that was generated based on your existing database.
  • docker-compose.yml: The Docker Compose file containing the configuration of your Prisma server, including details about how to connect to your database
  • prisma.yml: The root configuration file for your service

To be able to query your PostgreSQL database using GraphQL you now need to deploy the service:

prisma1 deploy

You can then view and edit your data in Prisma Admin or access it using the Prisma client.

Using prisma1 introspect

prisma1 introspect works in a similar way as the prisma1 init wizard in that you need to provide the database connection information.

While prisma1 init wizard generates an entire service configuration, prisma1 introspect only generates the datamodel file:

  • datamodel-[TIMESTAMP].prisma: The timestamp component allows you to use the introspect command for an existing Prisma service without overriding your existing datamodel.