Dependent Dropdown in Yii2 lost values on Update - yii2

Question

I created a form with a dropdownlist dependent on another (without extensions) and it ran fast.
But when you try to change the same form, the value of the second drop-down list is lost (type_id). Basically the Type field depends on the selected Area. See my code:
_form.php
<?= $form->field($model, 'area_id')->dropDownList(ArrayHelper::map(Department::find()->where(['helpdesk' => 1])->all(),'id','name'),['prompt'=>'Selecione a Área',
'onchange' => '
$.post("index.php?r=helpdesk/solicitation/lists&id=' . '"+$(this).val(),function(data){
$("select#solicitation-type_id").html(data);
});']) ?>
<?php
echo $form->field($model, 'type_id')->dropDownList(['prompt'=>'Selecione a Área']);
?>
Controller
public function actionLists($id)
{
$countType = Type::find()
->where(['area_id' => $id])
->count();
$types = Type::find()
->where(['area_id' => $id])
->orderBy(['name' => SORT_ASC])
->all();
if($countType > 0 )
{
foreach($types as $type ){
echo "<option value='".$type->id."'>".$type->name."</option>";
}
}
else{
echo "<option> - </option>";
}
}
I think it's the same problem at this topic, but I did not understand how it worked.

Answer 1

you need to provide the default set of options from which it should select the saved option whereas you are not providing any data
<?php
$types = Type::find()
->where(['area_id' => $model->area_id])
->orderBy(['name' => SORT_ASC])
->all();
echo $form->field($model, 'type_id')->dropDownList(ArrayHelper::map($types,'id','name'),['prompt'=>'Selecione a Área']);
?>
Now when you will use findOne() and select the model the saved value for the type_id will be automatically selected.
You can move the above query in the controller/action and pass the $types to the view.
also you can make you method actionLists D.R.Y by using count($types) and remove the first query
public function actionLists($id)
{
$types = Type::find()
->where(['area_id' => $id])
->orderBy(['name' => SORT_ASC])
->all();
if(count($types) > 0 )
{
foreach($types as $type ){
echo "<option value='".$type->id."'>".$type->name."</option>";
}
}
else{
echo "<option> - </option>";
}
}