Yii2 add tag to blog post - php

Question

I am totally confused about how should i save tag_id and post_id in the table when I still don't have the post_id. I made dropdownlist with options from database table
<?= Html::activeDropDownList($model, 'post_id', $ddItems, ['class' => 'form-control dd-list', 'prompt' => '']) ?>
That list contains tags(PHP, Java etc.).
User can have up to 3 tags on post. I tried to pass tags through GET and take in the controller with \Yii:$app->request->get(['id']) but without result.
my jQuery:
var ddList = $('.dd-list');
var tagList = $('.tag-container');
ddList.on('change', function () {
var tagHolder = document.createElement('div');
tagHolder.setAttribute('class', 'tag-holder');
var selected = $('.dd-list option:selected').text();
tagHolder.setAttribute('id', selected);
console.log(selected);
if(tagList.find('div').length > 2){
alert('You can have most 3 tags!');
return false;
}
if(tagList.find('#'+selected).length){
return false;
}else{
tagHolder.append(selected);
tagList.append(tagHolder);
$.ajax({
type : 'GET',
dataType : 'text',
url : '../post/create?tag=' + selected
});
}
});
actionCreate :
public function actionCreate()
{
$model = new Post();
$id = \Yii::$app->user->identity->id;
$ddItems = ArrayHelper::map(Tag::find()->all(),'tag_id', 'tag_name');
if ($model->load(Yii::$app->request->post())) {
date_default_timezone_set('Europe/Berlin');
$param = \Yii::$app->request->get();
$model->user_id = $id;
$model->date_create = date('m/d/Y');
if($model->save())
{
$tag = \Yii::$app->request->get(['tag']);
return $this->redirect(['view', 'id' => $model->post_id]);
}
throw new \yii\db\Exception("Some problem with DB connection ocurred!");
} else {
return $this->render('create', [
'model' => $model,
'ddItems' => $ddItems
]);
}
}
I am getting error : undefined tag. I am trying to get only one tag (because still don't know how to pass more).
What is the right way to reach my goal? I am in total mess from about 1 day! Ton of thanks in advance!
EDIT
I tried to send that tag with on click event like this :
$('.create-post').on('click', function () {
var tag = $('input[name=chosen-tag]').val();
console.log(tag);
$.ajax({
type : 'GET',
dataType : 'text',
url : '../post/create?tag=' + tag
});
});

Answer 1

I could not understand your programming scenario, But..
Change
$tag = \Yii::$app->request->get(['tag']);
To
$tag = \Yii::$app->request->get('tag');