Seed the database

Fill a database with sample data for development, or with the reference data every environment needs.

Before you start

Steps

1. Write seeders

A seeder is a name and a function. Use the db package inside it:

// Seeders fill a development database with sample data: go run . db:seed
var Seeders = []migrate.Seeder{
	{Name: "authors", Run: func(ctx context.Context) error {
		return db.CreateMany(ctx, []Author{
			{Name: "Ada", Email: "[email protected]"},
			{Name: "Grace", Email: "[email protected]"},
		})
	}},
	{Name: "posts", Run: func(ctx context.Context) error {
		ada, err := db.Query[Author](ctx).Where(AuthorCols.Email.Eq("[email protected]")).First()
		if err != nil {
			return err
		}
		now := anetos.Now(ctx).UTC()
		return db.CreateMany(ctx, []Post{
			{AuthorID: ada.ID, Title: "Hello, Anetos", Body: "The first post.", PublishedAt: &now},
			{AuthorID: ada.ID, Title: "A draft", Body: "Not published yet."},
		})
	}},
}

(Copied from examples/database/migrations.go, region seeders.)

AuthorCols holds the model’s typed columns, written by anetos gen.

For many rows, use a factory, the same one the tests use:

// Seeders add sample notes: go run . db:seed
var Seeders = []migrate.Seeder{
	{Name: "notes", Run: func(ctx context.Context) error {
		_, err := NoteFactory.CreateMany(ctx, 25) // see factories.go
		return err
	}},
}

(Copied from examples/forms/models.go, region seeders.)

In a project made with anetos new, factories go in database/factories and seeders in database/migrations.

2. Give them to the runner

// illustrative
runner, err := migrate.ForApp(app, []*migrate.Set{Migrations}, migrate.WithSeeders(Seeders...))

3. Run them

./app db:seed                 # every seeder, in order
./app db:seed --seeder=posts  # one of them
./app migrate:fresh --seed    # rebuild the database and seed it (development and testing only)

In production, db:seed needs --force.

How it works

Seeders run in the order they are listed, each in its own transaction: if one fails, its changes are rolled back and the ones before it stay. Order them so data exists before other data refers to it.

Coming from Laravel? A seeder is a Seeder class’s run method, and the list passed to the runner plays the role of DatabaseSeeder. Factories are values made with factory.New instead of classes.

Testing it

runner.Seed(ctx) in a test fills a fresh in-memory database, which is a quick way to test code against realistic data.

Common problems

Symptom	Cause	Fix
`no seeder named "users"`	Not in the list passed with `WithSeeders`	Add it
A seeder fails with a unique-constraint error on the second run	Seeders insert again each time	Use `db.Upsert`, or check with `Exists` first

Next steps

Migrations

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