Using SQL databases

Encore treats SQL databases as logical resources and natively supports PostreSQL databases. To start using a database you only need to define the schema by creating a migration file. Encore takes care of provisioning the database, running new schema migrations during deploys, and connecting to it.

Defining a database schema

Database schemas are defined by creating migration files in a directory named migrations within an Encore service package. Each migration file is named <number>_<name>.up.sql, where <number> is a sequence number for ordering the migrations and <name> is a descriptive name of what the migration does.

On disk it might look like this:

/my-app
├── encore.app                       // ... and other top-level project files
│
└── todo                             // todo service (a Go package)
    ├── migrations                   // todo service db migrations (directory)
    │   ├── 1_create_table.up.sql    // todo service db migration
    │   └── 2_add_field.up.sql       // todo service db migration
    ├── todo.go                      // todo service code
    └── todo_test.go                 // tests for todo service

Each migration runs in order and expresses the change in the database schema from the previous migration.

The file name format is important: Migration files must be sequentially named, starting with 1_ and counting up for each migration. Each file name must also end with .up.sql.

The first migration usually defines the initial table structure. For example, a todo service might start out by creating todo/migrations/1_create_table.up.sql with the following contents:

CREATE TABLE todo_item (
    id BIGSERIAL PRIMARY KEY,
    title TEXT NOT NULL,
    done BOOLEAN NOT NULL DEFAULT false
);

Provisioning databases

Encore automatically provisions databases to match what your application requires. When you define a database schema, Encore will provision the database at your next deployment.

Encore provisions databases in an appropriate way depending on the environment. When running locally, Encore creates a database cluster using Docker. In the cloud, it depends on the environment type:

• In production environments, the database is provisioned through the Managed SQL Database service offered by the chosen cloud provider.
• In development environments, the database is provisioned as a Kubernetes deployment with a persistent disk attached.

See exactly what is provisioned for each cloud provider, and each environment type, in the infrastructure documentation.

Inserting data into databases

Once you have defined a database schema, you can start inserting data into the database. Import encore.dev/storage/sqldb in your service package (or any sub-packages within the service). The interface is similar to that of the Go standard library's database/sql package, learn more in the package docs.

One way of inserting data is with a helper function that uses the package function sqldb.Exec. For example, to insert a single todo item using the example schema above, we can use the following helper function insert:

// insert inserts a todo item into the database.
func insert(ctx context.Context, id, title string, done bool) error {
	_, err := sqldb.Exec(ctx, `
		INSERT INTO todo_item (id, title, done)
		VALUES ($1, $2, $3)
	`, id, title, done)
	return err
}

Querying databases

To query a database in your application, you similarly need to import encore.dev/storage/sqldb in your service package or sub-package.

For example, to read a single todo item in the example schema above, we can use sqldb.QueryRow:

var item struct {
    ID int64
    Title string
    Done bool
}
err := sqldb.QueryRow(ctx, `
    SELECT id, title, done
    FROM todo_item
    LIMIT 1
`).Scan(&item.ID, &item.Title, &item.Done)

If sqldb.QueryRow does not find a matching row, it reports an error that can be checked against by importing the standard library errors package and calling errors.Is(err, sqldb.ErrNoRows).

Learn more in the package docs.

Connecting to databases

It's often useful to be able to connect to the database from outside the backend application. For example for scripts, ad-hoc querying, or dumping data for analysis.

The Encore CLI comes with built-in support for this:

• Use encore db shell [--env=<name>] <service-name> to open a psql shell to the database for <service-name> in the given environment. Leaving out --env defaults to the local development environment.

• Use encore db proxy [--env=<name>] to create a local proxy that forwards any incoming connection to the database in the given environment. Leaving out --env defaults to the local development environment.

See encore help db for more information on database management commands.

Handling migration errors

When Encore applies database migrations, there's always a possibility the migrations don't apply cleanly.

This can happen for many reasons:

• There's a problem with the SQL syntax in the migration
• You tried to add a UNIQUE constraint but the values in the table aren't actually unique
• The existing database schema didn't look like you thought it did, so the database object you tried to change doesn't actually exist
• ... and so on

If that happens, Encore records that it tried to apply the migration but failed. In that case, it's possible that one part of the migration was successfully applied but another part was not.

In order to ensure safety, Encore marks the migration as "dirty" and expects you to manually resolve the problem. This information is tracked in the schema_migrations table:

database=# \d schema_migrations
          Table "public.schema_migrations"
 Column  |  Type   | Collation | Nullable | Default
---------+---------+-----------+----------+---------
 version | bigint  |           | not null |
 dirty   | boolean |           | not null |
Indexes:
    "schema_migrations_pkey" PRIMARY KEY, btree (version)

To resolve the problem, you have two options: either revert back to the database schema from the previous migration (roll back), or fix the schema to match the new migration (roll forward).

Roll back

To roll back to the previous migration:

1. Use encore db shell <service-name> to log in to the database
2. Apply the necessary changes to the schema to revert it back to the previous migration version
3. Execute the query UPDATE schema_migrations SET dirty = false, version = version - 1;

Roll forward

To roll forward to the new migration:

1. Use encore db shell <service-name> to log in to the database
2. Apply the necessary changes to the schema to fix the migration failure and bring the schema up to date with the new migration
3. Execute the query UPDATE schema_migrations SET dirty = false;

Troubleshooting

Application won't run

When you run your application locally with encore run, Encore will parse and compile your application, and provision the necessary infrastructure including databases. If this fails with a database error, there are a few common causes.

Error: sqldb: unknown database

This error is often caused by a problem with the initial migration file, such as incorrect naming or location.

• Verify that you've created the migration file correctly, then try encore run again.

Error: could not connect to the database

When you can't connect to the database in your local environment, there's likely an issue with Docker:

• Make sure that you have Docker installed and running, then try encore run again.
• If this fails, restart the Encore daemon by running encore daemon, then try encore run again.

Error: Creating PostgreSQL database cluster Failed

This means Encore was not able to create the database. Often this is due to a problem with Docker.

• Check if you have permission to access Docker by running docker images.
• Set the correct permissions with sudo usermod -aG docker $USER (Learn more in the Docker documentation)
• Then log out and log back in so that your group membership is refreshed.