Yii - through relation, forms. How to implement?

Question

Yii

I'm completely confused, my head doesn't work, I can't save data to other models - I just don't understand what needs to be done.
Here I described how the models are made - another question . Please answer it too.
In general, I could not save the data in the PageCategoryPivot model, because I do not understand how to put it in the form (display the data by default), and then get new data and save it. With grief on the floor, I managed to edit the article (definitely not according to Feng Shui), but if you use the same form to create an article, it gives incomprehensible errors like

Fatal error: Call to a member function getErrors() on a non-object in C:\OpenServer\domains\framework\web\helpers\CHtml.php on line 2199

I think this is because when creating a model, a pure model is created, without a "pivot" connection, and it no longer fits the form where the data is displayed, so far, for the test, pivot-> cat_id. Although there may be other reasons.
Please tell me what should I do with this.

Answer 1

1. Why yii1 and not yii2?
2. Error with getErrors() because CHtml has no such method. We need to use activeForm to create validated forms.