在Yii2中使用预加载的连接实例

Question

I'm new to Yii, and experimenting with yii2's createCommand(), for this I've to create a new instance of the class yii\db\connection,

Here is an action in my controller,

public function actionDues($student_id){

    $connection = new \yii\db\Connection([
        'dsn' => 'mysql:host=localhost;dbname=db_school',
        'username' => 'root',
        'password' => '',
        'enableSchemaCache' => true,
    ]);
 $sql = 'select * from group_fees where group_id in (select group_id from group_subscriptions where subscriber_id='.$student_id.')';
 $command = $connection->createCommand($sql)->queryAll();

}

Am I right in thinking that there must be a connection instance already loaded, which I can use, instead of creating a new instance of the yii\db\connection class as above?

Answer 1

The db connection istance is normally create during the application boostrap phase by yii2 for this you set the related param in config/main.php or main-local (yii2-advanced template) or config/web.php -> db.php (in yii2 basic template)

   'components' => [
    'db' => [
        'class' => 'yii\db\Connection',
        'dsn' => 'mysql:host=your_host;dbname=your_dbdame;port=3306',
        'username' => 'root',
        'password' => 'your_pwd',
        'charset' => 'utf8',
        'enableSchemaCache' => true,            
    ],

and with this configuration you can use the db connection this way

$sql = "select a,b, from ..... your sql command';

Yii::$app->db->createCommand($sql)->execute()