Managing Postgres schema migrations and metadata (config v1)¶

Introduction¶

If you don’t already use any tool to manage your Postgres schema, you can use Hasura to do that for you. Hasura has a CLI which will help you save each action that you do on the console, including creating tables/views and schema modifying SQL statements, as YAML files. These files are called migrations and they can be applied and rolled back step-by-step. These files can be version controlled and can be used with your CI/CD system to make incremental updates.

Let’s say we have the following two tables in our schema:

author (id uuid, name text, rating integer)
article (id uuid, title text, content text, author_id uuid)

Now we want to set up migrations starting with this schema.

Before you begin¶

To use migrations effectively, the console on the server (which is served at /console) should be disabled and all changes must go through the console served by the CLI. Otherwise, changes could be made through the server console and they will not be tracked by migrations.

So, the first step is to disable the console served by the GraphQL engine server. In order to do that, remove the --enable-console flag from the command that starts the server or set the following environment variable to false:

HASURA_GRAPHQL_ENABLE_CONSOLE=false

Step 1: Install the Hasura CLI¶

Follow the instructions in Installing the Hasura CLI.

Step 2: Set up a project directory¶

For the endpoint referred here, let’s say you’ve deployed the GraphQL engine on Heroku, then this endpoint is: https://my-graphql.herokuapp.com. In case you’ve deployed Hasura using Docker, the URL might be http://xx.xx.xx.xx:8080. This endpoint should not contain the v1/graphql API path. It should just be the hostname and any sub-path if it is configured that way.

Let’s set up a project directory by executing the following command:

hasura init my-project --endpoint http://my-graphql.herokuapp.com

cd my-project

This will create a new directory called my-project with a config.yaml file and a migrations directory. This directory structure is mandatory to use Hasura migrations.

These directories can be committed to version control.

Step 3: Initialize the migrations (optional)¶

If you have previously set up your database, you need to initialize your migrations with the current state of the database.

Create a migration called init by exporting the current Postgres schema and metadata from the server:

# (available after version v1.0.0-alpha45)
# create migration files (note that this will only export the public schema from postgres)
hasura migrate create "init" --from-server

# note down the version

# mark the migration as applied on this server
hasura migrate apply --version "<version>" --skip-execution

This command will create a new migration under the migrations directory with the file name as <timestamp(version)>_init.up.yaml. This file will contain the required information to reproduce the current state of the server including the Postgres (public) schema and Hasura metadata. If you’d like to read more about the format of migration files, check out the Migration file format reference (config v1).

The apply command will mark this migration as “applied” on the server.

hasura migrate create "init" --from-server --schema "public" --schema "schema1" --schema "schema2"

Step 4: Use the console from the CLI¶

From this point onwards, instead of using the console at http://my-graphql.herokuapp.com/console you should use the console from the CLI by running:

# in project dir
hasura console

Step 5: Add a new table and see how a migration is added¶

As you use the Hasura console UI to make changes to your schema, migration files are automatically generated in the migrations/ directory in your project.

Let’s add the following table to our schema:

address (id uuid, street text, zip text, city text, country text)

In the migrations directory, you should now see a new migration created for the above statement.

Step 6: Apply the migrations on another instance of the GraphQL engine¶

Apply all migrations present in the migrations/ directory on a new instance at http://another-graphql-instance.herokuapp.com:

# in project dir
hasura migrate apply --endpoint http://another-graphql-instance.herokuapp.com

In case you need an automated way of applying the migrations, take a look at the CLI-Migrations Docker image, which can start the GraphQL engine after automatically applying the migrations which are mounted into a directory.

If you now open the console of the new instance, you can see that the three tables have been created and are tracked:

Step 7: Check the status of migrations¶

# in project dir
hasura migrate status

This command will print out each migration version present in the migrations directory and the ones applied on the database, along with a status text.

For example,

$ hasura migrate status
VERSION        SOURCE STATUS  DATABASE STATUS
1550925483858  Present        Present
1550931962927  Present        Present
1550931970826  Present        Present

Such a migration status indicates that there are 3 migration versions in the local directory and all of them are applied on the database.

If SOURCE STATUS indicates Not Present, it means that the migration version is present on the server, but not on the current user’s local directory. This typically happens if multiple people are collaborating on a project and one of the collaborators forgot to pull the latest changes which included the latest migration files or another collaborator forgot to push the latest migration files that were applied on the database. Syncing of the files would fix the issue.

If DATABASE STATUS indicates Not Present, it denotes that there are new migration versions in the local directory which are not applied on the database yet. Executing a migrate apply will resolve this.