db\ActiveRelationTrait via()

Specifies the relation associated with the junction table.

Use this method to specify a pivot record/table when declaring a relation in the yii\db\ActiveRecord class:

public function getOrders()
{
    return $this->hasOne(Order::className(), ['id' => 'order_id']);
}

public function getOrderItems()
{
    return $this->hasMany(Item::className(), ['id' => 'item_id'])
                ->via('orders');
}