# Migrations

Angel3 ORM ships with support for running database migrations, using a system modeled over [that of Laravel](https://laravel.com/docs/5.7/migrations).

An example is shown below:

```dart
class UserMigration implements Migration {
  @override
  void up(Schema schema) {
    schema.create('users', (table) {
      table
        ..serial('id').primaryKey()
        ..varChar('username', length: 32).unique()
        ..varChar('password')
        ..boolean('account_confirmed').defaultsTo(false);
    });
  }

  @override
  void down(Schema schema) {
    schema.drop('users');
  }
}
```

Migrations can be used to either create, alter, or drop database tables.

For more in-depth documentation, consult the `angel3_migration` documentation:

<https://github.com/dukefirehawk/angel/tree/master/packages/orm/angel_migration>

If you use `angel3_orm_generator`, then a migration will be generated by default for each class annotated with `@orm`.

To disable this:

```dart
@Orm(generateMigrations: false)
abstract class _MyModel extends Model {}
```

## Running Migrations

Using `package:angel3_migration_runner`, we can create executables that run our database migrations:

```dart
import 'package:angel3_migration_runner/angel3_migration_runner.dart';
import 'package:angel3_migration_runner/postgres.dart';
import 'package:postgres/postgres.dart';
import '../../angel3_migration/example/todo.dart';

var migrationRunner = PostgresMigrationRunner(
  PostgreSQLConnection('127.0.0.1', 5432, 'test'),
  migrations: [
    UserMigration(),
    TodoMigration(),
  ],
);
```

Running this file will produce output like the following:

```bash
Executes Angel3 migrations.

Usage: migration_runner <command> [arguments]

Global options:
-h, --help    Print this usage information.

Available commands:
  help       Display help information for migration_runner.
  refresh    Resets the database, and then re-runs all migrations.
  reset      Resets the database.
  rollback   Undoes the last batch of migrations.
  up         Runs outstanding migrations.

Run "migration_runner help <command>" for more information about a command.
```

The migration runner keeps track of a `migrations` table, in order to be able to keep track of which migrations it has run.


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