If you are coming over to Yii 2 from Yii 1.x, you may have already read this useful wiki for creating dependent dropdowns.
You can use a similar approach in Yii 2 to do the same. But if you are looking at a prebuilt solution that helps you manage it easier, read along.
You may have scenarios, where you want to store a specific array configuration to the database. A classic example could be saving Yii widget configuration to the database and then retrieving it at runtime, with dynamic parameters set. This wiki discusses one of the approaches to do this. Let's consider you have something like the NavBar configuration below to store in the db:
Sometimes we get lost trying to search by a HAS_MANY relation using CActiveRecord or CActiveDataProvider. This article is a series of drills that try to describe the practical techniques of searching by a HAS_MANY relation.
It's well known that there are Lazy Loading approach and Eager Loading approach in the relational query. But it's important to note that you should distinguish 2 different modes in the Eager Loading in Yii 1.1.x.