Serializing and Deserializing Data

DRF makes the process of building web API’s simple and flexible. With batteries included, it comes with well designed base classes which allows us to serialize and deserialize data.

Serialization and Deserialization

The first thing we need for our API is to provide a way to serialize model instances into representations. Serialization is the process of making a streamable representation of the data which we can transfer over the network. Deserialization is its reverse process.

Creating Serializers

Lets get started with creating serializer classes which will serialize and deserialize the model instances to json representations. Create a file named polls/serializers.py. We will use ModelSerializer which will reduce code duplication by automatically determing the set of fields and by creating implementations of the create() and update() methods.

Our polls/serializers.py looks like this.

from rest_framework import serializers

from .models import Poll, Choice, Vote


class VoteSerializer(serializers.ModelSerializer):
    class Meta:
        model = Vote
        fields = '__all__'


class ChoiceSerializer(serializers.ModelSerializer):
    votes = VoteSerializer(many=True, required=False)

    class Meta:
        model = Choice
        fields = '__all__'


class PollSerializer(serializers.ModelSerializer):
    choices = ChoiceSerializer(many=True, read_only=True, required=False)

    class Meta:
        model = Poll
        fields = '__all__'

The PollSerializer in detail

Our PollSerializer looks like this.

...

class PollSerializer(serializers.ModelSerializer):
    choices = ChoiceSerializer(many=True, read_only=True, required=False)

    class Meta:
        model = Poll
        fields = '__all__'

What have we got with this? The PollSerializer class has a number of methods,

  • A is_valid(self, ..) method which can tell if the data is sufficient and valid to create/update a model instance.
  • A save(self, ..) method, which khows how to create or update an instance.
  • A create(self, validated_data, ..) method which knows how to create an instance. This method can be overriden to customize the create behaviour.
  • A update(self, instance, validated_data, ..) method which knows how to update an instance. This method can be overriden to customize the update behaviour.

Using the PollSerializer

Let’s use the serializer to create a Poll object.

In [1]: from polls.serializers import PollSerializer

In [2]: from polls.models import Poll

In [3]: poll_serializer = PollSerializer(data={"question": "Mojito or Caipirinha?", "created_by": 1})

In [4]: poll_serializer.is_valid()
Out[4]: True

In [5]: poll = poll_serializer.save()

In [6]: poll.pk
Out[6]: 5

The poll.pk line tells us that the object has been commited to the DB. You can also use the serializer to update a Poll object.

In [9]: poll_serializer = PollSerializer(instance=poll, data={"question": "Mojito, Caipirinha or margarita?", "created_by": 1})

In [10]: poll_serializer.is_valid()
Out[10]: True

In [11]: poll_serializer.save()
Out[11]: <Poll: Mojito, Caipirinha or margarita?>

In [12]: Poll.objects.get(pk=5).question
Out[12]: 'Mojito, Caipirinha or margarita?'

We can see that calling save on a Serializer with instance causes that instance to be updated. Poll.objects.get(pk=5).question verifies that the Poll was updated.

In the next chapter, we will use the serializers to write views.