Serializers - Django REST Framework

In Django REST Framework (DRF), serializers convert complex data such as model instances or querysets into formats like JSON or XML for API responses.

• Transform database objects into JSON or other supported formats.
• Convert incoming JSON data back into Python types.
• Validate the input data before saving it to the database.
• Provide a clean way to control what data is exposed through an API.

Creating a Basic Serializer

To create a basic serializer, import serializers from rest_framework and define the fields to expose, similar to defining a Django form or model. 

from rest_framework import serializers
# create a serializer
class CommentSerializer(serializers.Serializer):
    # initialize fields
    email = serializers.EmailField()
    content = serializers.CharField(max_length = 200)
    created = serializers.DateTimeField()

Serializer can be declared for any entity or object based on the required fields.

Using Serializer to serialize data

A serializer such as CommentSerializer can be used to serialize a single comment or a list of comments. Using the Serializer class is similar to working with Django Forms.

Create a Comment class to represent a comment object that the serializer can process:

from datetime import datetime
# create a class
class Comment(object):
    def __init__(self, email, content, created = None):
        self.email = email
        self.content = content
        self.created = created or datetime.now()
# create a object
comment = Comment(email ='[email protected]', content ='foo bar')

After the object is created, open the Python shell and serialize the comment:

Python manage.py shell

Run the following code:

>>> from apis.serializers import CommentSerializer
>>> from datetime import datetime
>>> class Comment(object):
... def __init__(self, email, content, created=None):
... self.email = email
... self.content = content
... self.created = created or datetime.now()
...
>>> comment = Comment(email='[email protected]', content='foo bar')
>>> serializer = CommentSerializer(comment)
>>> serializer.data

Output:

ModelSerializer

A ModelSerializer n DRF provides a shortcut that automatically generates a serializer class based on a Django model.
It behaves like a regular Serializer but provides additional features such as:

• Automatic field generation from the model.
• Model-based validators like unique_together.
• Default implementations of .create() and .update() methods.

Syntax:

class SerializerName(serializers.ModelSerializer):
class Meta:
model = ModelName
fields = List of Fields

Example: Models.py

from django.db import models

class Account(models.Model):
  user_id = model.IntegerField()
  account_name = model.CharField(max_lenght=50)
  user = model.CharField(max_length=100)
  created = models.DateTimeField(auto_now_add=True)

Serializer:

class AccountSerializer(serializers.ModelSerializer):
    class Meta:
        model = Account
        fields = ['user_id', 'account_name', 'user', 'created']

By default, all model fields are automatically mapped to corresponding serializer fields. 

HyperlinkedModelSerializer

The HyperlinkedModelSerializer works similarly to ModelSerializer but represents relationships using hyperlinks instead of primary keys. Each object includes a url field that represents its unique endpoint, allowing easier navigation between related resources.

Syntax:

class SerializerName(serializers.HyperlinkedModelSerializer):
class Meta:
model = ModelName
fields = List of Fields

Example:

class AccountSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Account
        fields = ['id', 'account_name', 'users', 'created']

This approach makes the API responses more RESTful by using hyperlinks to connect related data.

Serializer Fields

Each field in a serializer works similarly to a Django form field, it handles validation, default values, error messages, and data representation.

Commonly Used Serializer Fields:

Note: NullBooleanField (a boolean field that allowed True, False, or NULL) is deprecated. Use BooleanField(null=True, blank=True) instead.

Core arguments in serializer fields

Each field in a Django REST Framework (DRF) serializer accepts a set of core arguments that control validation, default values, and data behavior.
These arguments allow developers to define how a field should behave during serialization (output) and deserialization (input).