Save multiple selections from a listbox - Yii2 - yii2

Question

I have made a Listbox depend on a dropDownList, when selecting an option from the dropDownList brings me a list of data that is added to the Listbox, it works to save a single option but the problem occurs when trying to save multiple selections, I cannot save more than 1 option, I have tried to add a foreach in my controller but it throws an error.
DropDownList
<?php echo $form->field($model, 'group_id')->widget(Select2::classname(), [
'data' => $seccion->lgrupo, //I get the group list
'size' => Select2::MEDIUM,
'theme' => Select2::THEME_BOOTSTRAP,
'options' => [
'placeholder' => '-- '.Yii::t('backend', 'Select').' --',
'onchange'=>'
$.post( "lists?id="+$(this).val(), function( data ) {//I get the list of people registered in the group and send it to the listbox
$( "select#assignment-user_id" ).html( data );
});',
],
'pluginOptions' => [
'allowClear' => true,
],
'addon' => [
'prepend' => [
'content' => Html::icon('building')
],
]
]); ?>
ListBox
<?php echo $form->field($model2, 'users_id')->listBox([] ,['multiple'=>true,'size'=>17]
); ?>
Groups Controller
public function actionCreate()
{
$model = new Groups();
$model2 = new Assignment();
$seccion = new Group();
if ($model->load(Yii::$app->request->post()) && $model2->load(Yii::$app->request->post())) {
if ($model->save(false)) {
foreach ($model2->users_id as $i => $as) {
$as->assign_group_id = $model->id_group_list;
if ($model2->save()) {
} else {
// error in saving model
}
}
return $this->redirect(['view', 'id' => $model->id_group]);
}
}
return $this->render('create', [
'model' => $model,
'model2' => $model2,
'seccion' => $seccion,
]);
}
Tables
I hope your can tell me what I'm doing wrong.

Answer 1

public function actionCreate()
{
$model = new Groups();
$model2 = new Assignment();
$seccion = new Group();
if ($model->load(Yii::$app->request->post()) && $model2->load(Yii::$app->request->post())) {
if ($model->save(false)) {
foreach ($model2->users_id as $user_id) {
$assignmentModel = new Assignment();
$assignmentModel->user_id= $user_id;
$assignmentModel->assign_group_id = $model->id_group_list;
//$assignmentModel->area= ''; //if you want to set some value to these fields
//$assignmentModel->assignment= '';
if ($assignmentModel->save()) {
} else {
// error in saving model
}
}
return $this->redirect(['view', 'id' => $model->id_group]);
}
}
return $this->render('create', [
'model' => $model,
'model2' => $model2,
'seccion' => $seccion,
]);
}