Reverse relationships in Nested serializer in django rest framework - django

Question

My models.py is as as follows:
class Group(models.Model):
name = models.CharField(max_length=50, unique=True)
class Policy(models.Model):
name = models.CharField(max_length=50, unique=True)
source_group = models.ForeignKey(Group, related_name='source_group')
destination_group = models.ForeignKey(Group, related_name='destination_group')
Since I have two foreign keys, pointing to the same model, I am using related name to avoid clashes.
Now, when I try to create a serializer for Groups in order to list all Policies associated with it, I do the following:
class PolicySerializer(serializers.ModelSerializers):
class Meta:
model = Policy
fields = "__all__"
class GroupSerializer(serializers.ModelSerializer):
policy = PolicySnippetSerializer(source ='source_group', many=True)
class Meta:
model = Group
fields = ['id', 'name', 'policy']
However, this will give me only policies for a a source_group.How did i get all groups associated with a group, source and destination ?

Answer 1

There can be two ways to do this.
Using SerializerMethodField.
By overriding data property method and appending the destination_group data into policy key.
Method 1:
class GroupSerializer(serializers.ModelSerializer):
policy = serializers.SerializerMethodField()
def get_policy(self, obj):
source_groups = PolicySnippetSerializer(obj.source_group.all(), many=True).data
destination_groups = PolicySnippetSerializer(obj.destination_group.all(), many=True).data
return source_groups + destination_groups
# rest of the code
Method 2:
class GroupSerializer(serializers.ModelSerializer):
policy = PolicySnippetSerializer(source ='source_group', many=True)
#property
def data(self):
serializer_data = super().data()
serializer_data['policy'] += PolicySnippetSerializer(self.instance.destination_group.all(), many=True).data
return serializer_data
# rest of the code