Convert to lowercase before saving?

Question

Yii

Good afternoon, I can't figure out how to keep the text in lower case: I
apply a filter:

public function rules()
    {
          ...
          ['username', 'filter', 'filter' => 'strtolower'],
    }

But saves all the same as entered by the user.
Most likely, I do not understand correctly how it works, and that the filter in the validation rules will not do this, but should I translate everything into beforeSave ?
Can you please tell me if the filter in the rules is applied or not?
how to implement it correctly

Answer 1

you can write like this:

['username', 'filter', 'filter' => function ($value) {
                return strtolower($value);
    }],