Django Rest Framework inserting and updating writable nested serializer - django

Question

I trying to insert and update a writable nested serializer with Django Rest Framework, following examples like this. But it doesn't work, because somehow after I execute serializer.is_valid() it lose the reference from serializer.validated_data like if it never was sent.
What could I having doing wrong?
My models
class User(AbstractUser):
institution = models.ForeignKey(Institution, on_delete=None, null=True, blank=True)
class Meta:
db_table = 'User'
managed = True
verbose_name = 'Users'
verbose_name_plural = 'Users'
ordering = ['id']
def __str__(self):
return self.email
class Institution(models.Model):
id = models.AutoField(db_column='id', primary_key=True)
name = models.CharField(db_column='name', max_length=255, null=False)
country = models.CharField(db_column='country', max_length=255, null=False)
class Meta:
db_table = 'Institution'
managed = True
verbose_name = 'Institutions'
verbose_name_plural = 'Institutions'
ordering = ['id']
def __str__(self):
return self.name
My serializers
class InstitutionSerializer(serializers.ModelSerializer):
class Meta:
model = Institution
fields = '__all__'
datatables_always_serialize = ('id', 'name', 'country')
class UserSerializer(serializers.HyperlinkedModelSerializer):
institution = InstitutionSerializer()
def create(self, validated_data):
return User.objects.create_user(**validated_data)
def update(self, instance, validated_data):
institution_data = validated_data['institution']
instance.institution = Institution.objects.get(pk=institution_data['id'])
return instance
class Meta:
model = User
fields = (
'id',
'username',
'first_name',
'last_name',
'email',
'password',
'is_active',
'institution',
)
datatables_always_serialize = (
'id',
'username',
'first_name',
'last_name',
'email',
'is_active',
'institution',
)
My view
class UserViewSet(ModelViewSet):
serializer_class = UserSerializer
permission_classes = (IsSuperUserPermission,)
def list(self, request, **kwargs):
params = Q()
if 'search[value]' in request.GET and request.GET['search[value]'] != '':
params = Q(username__icontains=request.GET['search[value]']) |\
Q(first_name__icontains=request.GET['search[value]']) |\
Q(last_name__icontains=request.GET['search[value]']) |\
Q(email__icontains=request.GET['search[value]']) |\
Q(institution__name__icontains=request.GET['search[value]'])
queryset = User.objects.filter(params).select_related().order_by('id')
serializer = self.serializer_class(queryset, many=True)
return Response(serializer.data)
def retrieve(self, request, *args, **kwargs):
queryset = User.objects.filter(pk=request.GET['pk']).select_related()
serializer = UserSerializer(queryset, many=True)
return Response(serializer.data)
def get_permissions(self):
if self.action in ('create',):
self.permission_classes = [AllowAny, ]
return super(self.__class__, self).get_permissions()
def create(self, request, *args, **kwargs):
serializer = UserSerializer(data=request.data)
if serializer.is_valid():
serializer.create(serializer.validated_data)
return Response(serializer.data)
else:
return Response(serializer.errors, status.HTTP_500_INTERNAL_SERVER_ERROR)
def partial_update(self, request, *args, **kwargs):
user = User.objects.get(pk=request.data['id'])
serializer = UserSerializer(instance=user, data=request.data, partial=True)
if serializer.is_valid():
if 'password' in serializer.validated_data:
serializer.validated_data['password'] = make_password(serializer.validated_data['password'])
serializer.update(user, serializer.validated_data)
return Response(serializer.data)
else:
return Response(serializer.errors, status.HTTP_500_INTERNAL_SERVER_ERROR)
Edit.
I submitting data like this:
{
"username": "BLA",
"email": "BLA#BLA.com",
"first_name": "BLA",
"last_name": "BLA",
"institution": 1,
"is_active": true,
"password": "bla12345"
}

Answer 1

Why this problem?
In your update payload, you are providing the institution data as an integer which represents the PK. But you've also defined a nested serializer InstitutionSerializer() inside UserSerializer() class. So, DRF expects a dict like object (DRF probably raise some error by mentioning so. I'm not sure why it's not happened in this situation).
What is the solution?
Since you are passing the institution id, I assume, you need the nested output only on HTTP GET requests. So, override the __init__() method of the UserSerializer() class and restrict the nested serializer usage to only HTTP GET requests
Here is the code
class UserSerializer(serializers.HyperlinkedModelSerializer):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if self.context['request'].method == 'GET':
self.fields['institution'] = InstitutionSerializer()
institution = InstitutionSerializer() # remove this
def create(self, validated_data):
return User.objects.create_user(**validated_data)
def update(self, instance, validated_data):
institution_data = validated_data['institution']
instance.institution = Institution.objects.get(pk=institution_data['id'])
return instance
class Meta:
model = User
fields = (
'id',
'username',
'first_name',
'last_name',
'email',
'password',
'is_active',
'institution',
)
datatables_always_serialize = (
'id',
'username',
'first_name',
'last_name',
'email',
'is_active',
'institution',
)
UPDATE-1
Change your partial_update() method of UserViewSet class as below,
def partial_update(self, request, *args, **kwargs):
user = User.objects.get(pk=request.data['id'])
serializer = UserSerializer(instance=user, data=request.data, partial=True, context={"request": request}) # change is here &lt&lt&lt
if serializer.is_valid():
if 'password' in serializer.validated_data:
serializer.validated_data['password'] = make_password(serializer.validated_data['password'])
serializer.update(user, serializer.validated_data)
return Response(serializer.data)
else:
return Response(serializer.errors, status.HTTP_500_INTERNAL_SERVER_ERROR)

Answer 2

I found a way to solve my problem, using JPG idea. I just add an else using a PrimaryKeyRelatedField to allow serializer to get reference from the model from id.
There might be another solution, bu this one works and looks better than multiple serializers.
class UserSerializer(serializers.HyperlinkedModelSerializer):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if self.context['request'].method == 'GET':
self.fields['institution'] = InstitutionSerializer()
else:
self.fields['institution'] = serializers.PrimaryKeyRelatedField(queryset=Institution.objects.all())