Validate checked checkbox quantity - yii2

Question

I have a voting form and I would like to validate the minimum and maximum number of candidates that each voter can vote for. These max and min values are stored in the logged user's session. What better way to do it?
MODEL Voto.php
public static function tableName()
{
return 'voto';
}
public function rules()
{
return [
[['eleicao_id', 'candidato_id', 'cargo_id', 'urna_id', 'created'], 'required','message'=> 'Selecione no mínimo 1 candidato!'],
[['eleicao_id', 'cargo_id', 'urna_id'], 'integer'],
[['created','candidato_id'], 'safe'],
[['eleitor_hash'], 'string', 'max' => 255],
];
}
FORM _form_votacao.php
<?php $form = ActiveForm::begin(); ?>
<div class="row">
<?php
$candidato = ArrayHelper::map(candidato::find()
->where(['status' => 1])
->Andwhere(['eleicao_id' => Yii::$app->user->identity->eleicao_id])
->orderBy("nome ASC")
->all(), 'id', 'nome'
);
echo $form->field($model, 'candidato_id')->checkboxList($candidato, [
'class' => 'h4',
'data-toggle' => 'button',
'item' => function($index, $label, $name, $checked, $value) {
return "<label class='col-md-5'><input type='checkbox' {$checked} name='{$name}' value='{$value}'> {$label}</label>";
}])->label(false);
?>
</div>
<br>
<div class="row text-center">
<div class="form-group">
<?= Html::submitButton('Confirmar', ['class' => 'btn btn-success']) ?>
</div>
</div>
<?php ActiveForm::end(); ?>
Note: This list of candidates is dynamic, loads the candidates according to the parameters of the user logged in.
Rules Test UPDATE:
public function rules()
{
return [
['candidato_id', 'validateCandidates','message'=> 'teste'],
];
}
public function validateCandidates($attribute, $params, $validator){
if(count($this->candidato_id) >= 4){ // test with value 4
$this->addError($attribute, 'Error message');
}
}

Answer 1

Create custom validation. Something like this:
Model Voto.php
public function rules()
{
return [
....
['candidato_id', 'validateCandidates'],
....
];
}
public function validateCandidates($attribute, $params, $validator){
if(count($this->candidato_id) < {session_min} and count($this->candidato_id) > {session_max}){
$this->addError($attribute, 'Error message');
}
}