Using SQL databases

Encore treats SQL databases as logical resources. This means using a database only requires you to define the schema and then start using it. Encore takes care of provisioning the database, running new schema migrations during deploys, and connecting to it.

Encore's SQL databases are PostgreSQL databases.

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.

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

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
);

Querying databases

Once you have defined a database schema, you can easily query it. Simply import encore.dev/storage/sqldb in your service package (or any sub-packages within the service), and start using the package functions. The interface is similar to that of the Go standard library's database/sql package.

For example, to read a single todo item using the example schema above:

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)

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.

Provisioning databases

Encore automatically provisions databases in a suitable way depending on the environment. When running locally, Encore creates a database cluster using docker. In the cloud, how the database is provisioned depends on the type of Encore Environment:

• 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.

Encore automatically provisions databases to match what your application requires. Simply define a database schema (see above) and Encore will provision the database at the start of the next deploy.

Handling migration errors

When Encore applies database migrations — both locally when developing as well as when deploying to the cloud — there's always the 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

When 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;