Module Validation under certain condition yii2

[meriah]

I want to test the field for uniqueness only if it's available, how am I supposed to put it in the rules? I'm doing this.

public function rules()
{
    return [
       ['checked_box', 'unique',
           'on' => 'Только при наличии этого поля в модели'
       ],
    ];
}

How am I supposed to write a simple condition?

[authera]

In default if the field is empty, the rule does not apply ( http://www.yiiframework.com/doc-2.0/yii-validators-validator.html#$skipOnEmpty-detail other question as he checks, empty field or not. You can redesign the method of checking the void. http://www.yiiframework.com/doc-2.0/yii-validators-validator.html#$isEmpty-detail And watch https://github.com/yiisoft/yii2/blob/master/framework/validators/Validator.php#L372

public function rules()
{
    return [
       [
        'checked_box',
        'unique',
        'isEmpty'=>function($value){ return isset($value); },
        'on' => 'Только при наличии этого поля в модели'
       ],
    ];
}