====== DB: Abfragen ======

<code php>
// return a single customer whose ID is 123
// SELECT * FROM `customer` WHERE `id` = 123
$customer = Customer::find()
    ->where(['id' => 123])
    ->one();

// return all active customers and order them by their IDs
// SELECT * FROM `customer` WHERE `status` = 1 ORDER BY `id`
$customers = Customer::find()
    ->where(['status' => Customer::STATUS_ACTIVE])
    ->orderBy('id')
    ->all();

// mit 2 Order-By:
$model::find()->orderBy([
  'id_date' => SORT_DESC,
  'item_no'=>SORT_ASC
]);

// return the number of active customers
// SELECT COUNT(*) FROM `customer` WHERE `status` = 1
$count = Customer::find()
    ->where(['status' => Customer::STATUS_ACTIVE])
    ->count();

// return all active customers in an array indexed by customer IDs
// SELECT * FROM `customer`
$customers = Customer::find()
    ->indexBy('id')
    ->all();

// Grösser/kleiner als
return Country::find()
        ->where(['>=', 'population', $lower])
        ->andWhere(['<=', 'population', $upper])
        ->all();
</code>

====== Select für Dropdown ======
<code php>
    $items = ArrayHelper::map(Datatables::find()->select(['datatable_id', 'datatable_name'])->asArray()->all(), 'datatable_id', 'datatable_name'); 
    
    echo $form->field($model, 'datatable_id')->dropdownList($items,
    	['prompt'=>'...']
	);
</code>

===== Eager Loading =====
<code php>
$player = PlayersModel::find()->where(['id' => $id])->with('club')->one();

        $class = Classes::find()->where(['id' => $class_id])->with('dancesClasses', 'dancesClasses.dances')->one();
</code>