Serializers allow complex data like querysets and model instances to be converted to native Python datatypes that can then be easily rendered into JSON, XML, and other formats.
Using ModelSerializer class:
Suppose we wanted to create a PostSerializer for our example Post model and CommentSerializer for our Comment model.
class PostSerializer(serializers.ModelSerializer):
class Meta:
model = Post
fields = ('id', 'title', 'text', 'created')
class CommentSerializer(serializers.ModelSerializer):
class Meta:
model = Comment
fields = ('post', 'user', 'text')
Or also you could use exclude
to exclude certain fields from being seialized. ModelSerializer has default implementations for the create()
and update()
methods.
Nested Serialization
By default, instances are serialized with primary keys to represent relationships. To get nested serialization we could use, General or Explicit methods.
General
Using depth
parameter.
class CommentSerializer(serializers.ModelSerializer):
class Meta:
model = Comment
fields = '__all__'
depth = 2
Explicit
Yuo can also define and nest serializers within eachother…
class CommentSerializer(serializers.ModelSerializer):
post = PostSerializer()
class Meta:
model = Comment
fields = '__all__'
So here, the comment’s post
field (how we named it in models.py) will serialize however we defined it in PostSerializer
.
HyperlinkedModelSerializer
This makes your web API a lot more easy to use (in browser) and would be a nice feature to add.
Let’s say we wanted to see the comments that every post has in each of the Post instances of our API.
With HyperlinkedModelSerializer
, instead of having nested primary keys or nested fields, we get a link to each individual Comment (URL).
class PostSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = Post
fields = ('id', 'title', 'text', 'created', 'comments')
read_only_fields = ('comments',)
Note: without the read_only_fields
, the create
form for Posts would always require a comments
input, which doesn’t make sense (comments on a post are normally made AFTER the post is created).
Another way of hyperlinking is just adding a HyperlinkedRelatedField
definition to a normal serializer.
class PostSerializer(serializers.ModelSerializer):
comments = serializers.HyperlinkedRelatedField(many=True, view_name='comment-detail', read_only=True)
class Meta:
model = Post
fields = ('id', 'title', 'text', 'created', 'comments')
Dynamically modifying fields in the serializer
This makes your web API a lot more easy for extract limited number of parameter in response. Let’s say you want to set which fields should be used by a serializer at the point of initialization.
Just copy below code and past it in your serliazer file
class DynamicFieldsModelSerializer(serializers.ModelSerializer):
def __init__(self, *args, **kwargs):
# Don't pass the 'fields' arg up to the superclass
fields = kwargs.pop('fields', None)
# Instantiate the superclass normally
super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)
if fields is not None:
# Drop any fields that are not specified in the `fields` argument.
allowed = set(fields)
existing = set(self.fields.keys())
for field_name in existing - allowed:
self.fields.pop(field_name)
Extend DynamicFieldsModelSerializer
from your serializer class
class UserSerializer(DynamicFieldsModelSerializer):
class Meta:
model = User
fields = ('id', 'username', 'email')
Mention the fields name inside fields
UserSerializer(user, fields=('id', 'email'))
Here, you will get only id
and email
from serializer instead of all.