Software Development

Decide serializer class dynamically based on viewset actions in Django Rest Framework (DRF)

Practically and for most cases that I have observed, it so happens that an application tends to expose only required information based on what a client asks (requests) the resource. Hence the application needs different serializer classes based on the requirement at the time of writing APIs in DRF.

For instance, to get the list of users in pagination style, you may simply be interested in showing their names, email IDs, and the organization they’re working for. But for a specific user’s detailed view you might want to give other information as well such as addresses, phone numbers, job title, department, record creation/modification time, and record created/modified by whom, etc.

Let’s start with Company and User models defined in the gist as follows:

User model has been extended from Common & AbstractUser models and has a field company refers to Company which means mostly each user (except is_superuseris_staff members) should belong to a company with at least SYS_USER role.

Now, let’s create a few serializer classes for these models as follows:

Here, we created two serializer classes for each model, one for listing purpose and another one for detailed lookup.

Now, your application wants to use UserSerializer when the client hits the /users/ API endpoint and UserDetailSerializer for the/users/{pk}/ API endpoint. Under a viewset you can do this by overriding get_serializer_class method. You can introduce a new variable serializer_action_classes along with serializer_class under a viewset which maps the viewset action name to serializer class. Now, your overridden get_serializer_class will look like,

overriding get_serializer_class method | the image created using https://carbon.now.sh tool

If an API endpoint matches to viewset action (e.g, /users/ API endpoint to listviewset action) then the serializer class will be used if it’s defined in serializer_action_classes variable else it will fall back to use serializer_class, the default one. You can create mixin for this so that you can use the functionality in other viewsets too without overriding get_serializer_classmethod under each viewset. So, the mixin GetSerializerClassMixin would look like as follows:

Now, you just have to inherit GetSerializerClassMixin class in your viewset classes and just mention the serializer_action_class variable so that our final viewset code would like:


Okay! But I want to limit the user’s information based on the current session user role.

Let’s say Frank and Joe belong to a company called RainDrops with roles SYS_ADMIN and SYS_USER respectively. Note that this allows Frank to manage all users under RainDrops company. Therefore, Frank is able to see full details (UserDetailSerializer data) of all users from RainDrops company whereas Joe is able to see only limited info (UserSerializer data). Also, Frank and Joe both are able to see only limited information of a user that is not part of RainDrops company.

Okay, this is a very special case which I came across during one of my projects. For the assignment, I had to write custom logic by overriding get_serializer_class method, had to dig into DRF source code by taking help from some of code through drf-extensions as well.

In case you noticed, in the above gist, we’re no longer using GetSerializerClassMixin class for the inheritance plus I changed the value of serializer_class to UserSerializer with serializer_detail_class = UserDetailSerializer as an additional variable. In the above code, we’re getting detailed value from the URL (e.g, /users/2/ => 2) using lookup from kwargs and then using this value we get the user instance. The logic will use serializer_detail_class in two cases: to send the detailed info of a user or use serializer_class for limited info of a user which are as follows:

  1. If current session user is looking for their own profile (when Frank or Joe is looking into his data).
  2. If a user (with the SYS_ADMIN role) is looking at other users for the same company (when Frank is looking at Joe’s data).

Credits and References

The credit for using a mixin to choose serializer class per viewset action goes to the two links (posted below), my role was limited to simplifying and explaining it step by step :). Additionally, I covered the special case about limiting on delivering data to clients (with Frank and Joe example). The focus of this article is to deal with what kind of information your APIs want to deliver to clients with simple as well as special use-cases based on viewset action.

 
 

 

I hope this will help to deal with the problems similarly I had. The entire sample source code is available at this repository. Thank you for reading the article.

author
Sudip Raval
Full Stack Software Engineer [Python | Django | JavaScript | Docker] (7+ years) working with Aubergine Solutions Pvt. Ltd. Experienced in web application development. Strong hand on Python, Golang, JavaScript programming languages and Django, VueJS frameworks.