Sometimes the endpoints you get when you use a ModelViewSet aren't enough and you need to add extra endpoints for custom functions. To do this, you could use the APIView class and add a custom route to your `urls.py` file, and that would work fine.

But if you have a viewset already, and you feel like this new endpoint belongs with the other endpoints in your viewset, you can use DRF's @action decorator to add a custom endpoint. This means you don't have to change your urls.py -- the method you decorate with your @action decorator will automatically be rendered along with the other enpdoints.

If you came here from Part 1 of What You Should Know About Django REST Framework, you may be wondering why I just walked you through a bunch of source code. We stepped through that code because if you know what the main methods of the ModelViewSet do and how they work, you know where to go when you want to tweak the behavior of your viewset. You can pull out the method that contains what you want to change, override it with your own custom behavior, and put it back in. In Part 1, we were writing a BookViewSet. So let's go through a few cases where we might want to customize the behavior of our endpoints and walk through how we would do that.

One of the things I hear people say about Django is that it's a "batteries included" framework, and Django REST Framework is no different. One of the most powerful of these "batteries" is the ModelViewSet class, which is more of a "battery pack," in that it contains several different batteries. If you have any experience with Django's class-based views, then DRF's viewsets will hopefully look familiar to you.