If you develop rather complex applications with Yii2, you might already be familiar with yii2-app-advanced application template. Well, the template is awesome and provides high flexibility regarding code/configuration sharing among parts of an application.
I have read http://www.yiiframework.com/wiki/24/creating-a-dependent-dropdown/ (Dependen Dropdown Yii1), but I can't implement it in Yii2 because Yii2 does not have built-in AJAX functionality hem.. I searched about it and came across this post
Here is a example on how to use Pjax with GridView (yii\grid\GridView) and ActiveForm (yii\widgets\ActiveForm) widgets in Yii2.
There are a few issues with the other solutions I originally used that I found from other wikis. I address the issues I had in this much simpler and shorter way. I am also going to explain what is going into way more detail than others to help people understand what's going on.
One of the things you will find tricky to implement is the the sorting and filtering of a GridView's column that displays related model data.