A Sample Code
=============

The following is the code that constructs a page that gathers a user's favorite foods.

Here are 4 models involved in this page.

1. User extends ActiveRecord

   - id
   - name
   - ... etc.
   
2. Food extends ActiveRecord

   - id
   - name
   - ... etc.

3. FavoriteFood extends ActiveRecord

   - user_id
   - food_id

4. UserFovorites extends Model

   - user_id
   - food_ids

Note that the last one is **not** an ActiveRecord, and **'food_ids' attribute is an array** of food ids. We use this model for the form of the page.

Model
-----

Please take note that **`EachValidator`** is used to validate the array of `food_ids` attribute.

```php
class UserFavorites extends Model
{
    /**
     * @var integer
     */
    $user_id;

    /**
     * @var array IDs of the favorite foods
     */
    $food_ids = [];
    
    /**
     * @return array the validation rules.
     */
    public function rules()
    {
        return [
            ['user_id', 'required'],
            ['user_id', 'exist', 'targetClass' => User::className(), 'targetAttribute' => 'id'],
            // each food_id must exist in food table
            ['food_ids', 'each', 'rule' => [
                'exist', 'targetClass' => Food::className(), 'targetAttribute' => 'id'
            ]],
        ];
    }

    /**
     * @return array customized attribute labels
     */
    public function attributeLabels()
    {
        return [
            'user_id' => 'User',
            'food_ids' => 'Favorite Foods',
        ];
    }

    /**
     * load the user's favorite foods
     */
    public function loadFavorites()
    {
        $this->food_ids = [];
        $favfoods = FavoriteFood::find()->where(['user_id' => $this->user_id])->all();
        foreach($favfoods as $ff) {
            $this->food_ids[] = $ff->food_id;
        }
    }

    /**
     * save the user's favorite foods
     */
    public function saveFavorites()
    {
        FavoriteFood::deleteAll(['user_id' => $this->user_id]);
        if (is_array($this->food_ids)) {
            foreach($this->food_ids as $food_id) {
                $ff = new FavoriteFood();
                $ff->user_id = $this->user_id;
                $ff->food_id = $food_id;
                $ff->save();
            }
        }
        /* Be careful, $this->food_ids can be empty */
    }

    /**
     * @return array available foods
     */
    public static function getAvailableFoods()
    {
        $foods = Food::find()->order('name')->asArray()->all();
        $items = ArrayHelper::map($foods, 'id', 'name');
        return $items;
    }
}
```

Controller
----------

```php
public function actionFavoriteFood($user_id)
{
    $model = new UserFavorites();
    $model->user_id = $user_id;
    
    if ($model->load(Yii::$app->request->post()) {
        if ($model->validate()) {
            $model->saveFavorites();
            return $this->redirect(['index']);
        }
    }
    $model->loadFavorites();
    $items = UserFavorites::getAvailableFoods();
    return $this->render('favorite', [
        'model' => $model,
        'items' => $items,
    ]);
}
```

View
----

```php
<?php $form = ActiveForm::begin([
    'id' => 'favorite-form',
    'enableAjaxValidation' => false,
]); ?>

<?= Html::activeHiddenInput($model, 'user_id') ?>

<?php echo $form->field($model, 'food_ids')->widget(DualListbox::className(),[
        'items' => $items,
        'options' => [
            'multiple' => true,
            'size' => 15,
        ],
        'clientOptions' => [
            'nonSelectedListLabel' => 'Available Foods',
            'selectedListLabel' => 'Favorite Foods',
            'moveOnSelect' => false,
        ],
    ])
    ->hint('Select the favorite foods.');
?>

<div class="form-group">
    <?= Html::submitButton('Update', [
        'class' => 'btn btn-primary'
    ]) ?>
</div>

<?php ActiveForm::end(); ?>
```