Each child class of Migration represents an individual MongoDB migration which
is identified by the child class name.
Within each migration, the [[up()]] method should be overridden to contain the logic
for "upgrading" the database; while the [[down()]] method for the "downgrading"
logic.
Migration provides a set of convenient methods for manipulating MongoDB data and schema.
For example, the Migration::createIndex method can be used to create a collection index.
Compared with the same methods in Collection, these methods will display extra
information showing the method parameters and execution time, which may be useful when
applying migrations.
public function setUp()
{
$this->migrateControllerClass = MigrateController::className();
$this->migrationBaseClass = Migration::className();
parent::setUp();
$this->setUpMigrationPath();
Yii::$app->setComponents(['mongodb' => $this->getConnection()]);
}
