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Django - Pass variable to serializer which gets used in calculating a serializers.SerializerMethodField?

So I have this serializer that adds an attribute. Let's say I want to serialize Post data, which is like a post on Facebook or Twitter. When I serialize it lets say I want to pass a variable to the serializer region, because I use that variable to calculate an attribute in the Serializer that I want. So for example I'd like to do something like PostSerializer(post_object, region='Italy') and it'll use region='Italy' for calculating an attribute which is a serializers.SerializerMethodField. How can I pass a variable to my serializer that is used to calculae a serializers.SerializerMethodField()?
serializer.py
class PostSerializer(serializers.ModelSerializer):
post_count_from_region = serializers.SerializerMethodField()
class Meta:
model = Post
fields = ('author', 'body', 'created', 'updated_at', 'post_count_from_region')
def get_post_count_from_region(self, post_obj, region:str):
return Post.objects.filter(region=region).count()
So for a more explicit example of what this use case looks like is:
view.py
def get_full_post_data_by_uuid(request, post_uuid, region: str):
post_obj = Post.objects.get(pk=post_uuid)
return Response(PostSerializer(post_obj, region=region).data, status=200)

So this is what context is for in Serializers on Django. context takes in a dictionary so you can do.
PostSerializer(post_object, context={'region':'Italy'})
then under serializer
def get_post_count_from_region(self, post_obj):
region = self.context.get('region', <default value>)
return Post.objects.filter(region=region).count()

I receive typerror when use request method in drf

With some help, I solved this issue.
My api is work, but today I found this error when I try to access '/api/v1/docs'
AttributeError at /api/v1/docs/
'NoneType' object has no attribute 'method'
I know that the error is here:
def get_fields(self):
fields = super().get_fields()
if self.context['request'].method in ['POST', 'PATCH', 'PUT']:
fields['products'] = serializers.ListField(
write_only=True,
child=serializers.IntegerField()
)
return fields
When I remove .method, the access to the /api/v1/docs/ works, but my solution to post some products in bundleproducts, doesn't work.
My code:
view.py
class ProductViewSet(viewsets.ModelViewSet):
queryset = Product.objects.all()
serializer_class = ProductSerializer
model = Product
class BundleProductViewSet(viewsets.ModelViewSet):
queryset = BundleProduct.objects.all()
serializer_class = BundleProductSerializer
model = BundleProduct
class BundleViewSet(viewsets.ModelViewSet):
queryset = Bundle.objects.all()
serializer_class = BundleSerializer
model = Bundle

This is probably caused by this serializer being used as a nested serializer in another serializer. So lets say the definition for the serializer in question is:
class MySerializer(serializers.Serializer):
...
And you have another serializer like this:
class OtherSerializer(serializers.Serializer):
my_field = MySerializer()
In this case, when instantiating an instance of OtherSerializer, its context is not passed automatically to MySerializer, so there would not be a request in the context of MySerializer. You can either add the context to nested serializer manually, or in the get_fields method, check that request exists in self.context and proceed accordingly.
Also, I am not sure what you are trying to accomplish, but if you provide a field with
write_only=True
in serializer class definition, the field would not be present when reading the serializer, i.e for get requests in general, which seems like what you are trying to do here. So adding the products field as write_only would have the same effect, you do not need to override get_fields method

how to set foreignkey value in child serializer in django rest framework when the parent record exists

I have two models first as parent model "Country", that filled before the second one as child model "City". as the following
class Country(models.Model):
name = models.CharField(max_length=35)
icon = models.ImageField()
def __str__(self):
return self.name
class City(models.Model):
name = models.CharField(max_length=35)
country = models.ForeignKey(to=Country, on_delete=models.CASCADE)
def __str__(self):
return self.name
My serializers.py for my need as following :
class CountrySerializer(ModelSerializer):
class Meta:
model = Country
fields = '__all__'
class CitySerializer(ModelSerializer):
country = serializers.PrimaryKeyRelatedField(queryset=Country.objects.all())
class Meta:
model = City
fields = ('name', 'country')
view.py
class CountryAPIView(ListAPIView):
queryset = Country.objects.all()
serializer_class = CountrySerializer
permission_classes = [AllowAny, AllowAnonymous]
class CityAPIView(ListAPIView):
queryset = City.objects.all()
serializer_class = CitySerializer
permission_classes = [AllowAny, AllowAnonymous]
def post(self, request):
serializer = CitySerializer(data=request.data)
if serializer.is_valid(raise_exception=ValueError):
serializer.create(validated_data=request.data)
return Response(serializer.data, status=status.HTTP_201_CREATED)
return Response(serializer.error_messages,
status=status.HTTP_400_BAD_REQUEST)
now when i run get api it run and gives me a result fine . But when im trying to create a new city and set "country":"id" in json i got this error
Cannot assign "2": "City.country" must be a "Country" instance.
So if i was not clear ,, what i need is exactly set foreign key to city when i create city ,, not create city and country,,
please any one had a solution help, because i tried many ways and read the django rest framework docs about this point but i didn't got it.

First of all, the raise_exception should be a boolean value (either True or False)
You could avoid this error by using inheriting the view class from ListCreateAPIView
from rest_framework.generics import ListCreateAPIView
class CityAPIView(ListCreateAPIView):
queryset = City.objects.all()
serializer_class = CitySerializer
permission_classes = [AllowAny, AllowAnonymous]
You don't want to use the post() method if you're using ListCreateAPIView, because DRF will take care of that part well.
Suggestion
Since you're dealing with CRUD functionalities of the model, you can use the DRF's ModelViewset class

you are not using the validated data to create a new city, just change this line:
serializer.create(validated_data=request.data)
to this:
serializer.save()
when you perform serializer.save(), the serializer will use its validated data.
also, DRF has a generic view(ListCreateAPIView) that covers your use-case.

Get current user in Model Serializer

Is it possible to get the current user in a model serializer? I'd like to do so without having to branch away from generics, as it's an otherwise simple task that must be done.
My model:
class Activity(models.Model):
number = models.PositiveIntegerField(
blank=True, null=True, help_text="Activity number. For record keeping only.")
instructions = models.TextField()
difficulty = models.ForeignKey(Difficulty)
categories = models.ManyToManyField(Category)
boosters = models.ManyToManyField(Booster)
class Meta():
verbose_name_plural = "Activities"
My serializer:
class ActivitySerializer(serializers.ModelSerializer):
class Meta:
model = Activity
And my view:
class ActivityDetail(generics.RetrieveUpdateDestroyAPIView):
queryset = Activity.objects.all()
serializer_class = ActivityDetailSerializer
How can I get the model returned, with an additional field user such that my response looks like this:
{
"id": 1,
"difficulty": 1,
"categories": [
1
],
"boosters": [
1
],
"current_user": 1 //Current authenticated user here
}

I found the answer looking through the DRF source code.
class ActivitySerializer(serializers.ModelSerializer):
# Create a custom method field
current_user = serializers.SerializerMethodField('_user')
# Use this method for the custom field
def _user(self, obj):
request = self.context.get('request', None)
if request:
return request.user
class Meta:
model = Activity
# Add our custom method to the fields of the serializer
fields = ('id','current_user')
The key is the fact that methods defined inside a ModelSerializer have access to their own context, which always includes the request (which contains a user when one is authenticated). Since my permissions are for only authenticated users, there should always be something here.
This can also be done in other built-in djangorestframework serializers.
As Braden Holt pointed out, if your user is still empty (ie _user is returning None), it may be because the serializer was not initialized with the request as part of the context. To fix this, simply add the request context when initializing the serializer:
serializer = ActivitySerializer(
data=request.data,
context={
'request': request
}
)

A context is passed to the serializer in REST framework, which contains the request by default. So you can just use self.context['request'].user inside your serializer.

I had a similar problem - I tried to save the model that consist user in, and when I tried to use
user = serializers.StringRelatedField(read_only=True, default=serializers.CurrentUserDefault()) like on official documentation - but it throws an error that user is 'null'. Rewrite the default create method and get a user from request helped for me:
class FavoriteApartmentsSerializer(serializers.ModelSerializer):
user = serializers.StringRelatedField(read_only=True, default=serializers.CurrentUserDefault())
class Meta:
model = FavoriteApartments
exclude = (
'date_added',
)
def create(self, validated_data):
favoriteApartment = FavoriteApartments(
apartment=validated_data['apartment'],
user=self.context['request'].user
)
favoriteApartment.save()
return favoriteApartment

I modified the request.data:
serializer = SectionSerializer(data=add_profile_data(request.data, request.user))
def add_profile_data(data, user):
data['user'] = user.profile.id
return data

Django Rest Order on custom field from serializer?

I'm trying to use Django Rest to return a json representation of a model based on a ordering from a custom field that is not attached to the model, but is attached to the serializer. I know how to do this with model specific fields, but how do you use django rest to return an ordering when the field is only within the serializer class? I want to return a list of Pics ordered by 'score'. Thanks!
------Views.py
class PicList(generics.ListAPIView):
queryset = Pic.objects.all()
serializer_class = PicSerializerBasic
filter_backends = (filters.OrderingFilter,)
ordering = ('score')
------Serializer.py
class PicSerializer(serializers.ModelSerializer):
userprofile = serializers.StringRelatedField()
score = serializers.SerializerMethodField()
class Meta:
model = Pic
fields = ('title', 'description', 'image', 'userprofile', 'score')
order_by = (('title',))
def get_score(self, obj):
return Rating.objects.filter(picc=obj).aggregate(Avg('score'))['score__avg']

You could move the logic of the method get_score to the manager of the class Pic. In this answer there is an example of how to do it.
Once you have it in the manager, the score field would become "magically" available for every object of the class Pic everywhere (serializer, views...) and you'll be able to use it for ordering.