I am attempting to add context to a serializer within a ModelViewSet which is dependent on the current paged object list in context. I'll explain with an example.
I am building a viewsets.ModelViewSet that lists Users and a list of favorite_foods. However- the list of user's favorite foods in some external microservice accessible via API. Building a ViewSet to collect objects and performing HTTP requests on each is trivial, we can do something like this:
class UserViewSet(viewsets.ViewSet):
queryset = User.objects.all()
serializer_class = UserSerializer
class UserSerializer(serializers.ModelSerializer):
favorite_foods = serializers.SerializerMethodField()
def get_favorite_foods(self, instance):
# performs an HTTP call and returns a list[] of foods.
return evil_coupled_microservice_client.get_user_food_list(instance)
class Meta:
model = User
fields = ('id', 'name', 'favorite_foods')
The issue is (aside from some ugly infrastructure coupling) this is going to make an HTTP request count equivalent to the page size. Instead- it would be great if I could prefetch the favorite food lists for all users on the page in a single HTTP call, and just add them into context, like this:
class UserViewSet(viewsets.ViewSet):
def get_serializer_context(self):
context = super().get_serializer_context()
users = <-- This is where I want to know what users are in the current filtered, paginated response.
users_food_dict = evil_coupled_microservice_client.get_many_users_food_list(users)
context.update({'usesr_foods': users_food_dict})
return context
However- it doesn't appear there is any way to fetch the object list that's going to be serialized. Although (I'm fairly sure) get_serializer_context is called after the queryset is filtered and paginated, I'm not sure how to access it without doing some really hacking re-compiling of the queryset based on the query_params and other pieces attached to the class.
I'll post my current solution. It's not terrible, but I'm still hoping for a cleaner built-in.
class UserViewSet(viewsets.ViewSet):
...
def list(self, request, *args, **kwargs):
# Overrwite `ListModelMixin` and store current set
queryset = self.filter_queryset(self.get_queryset())
page = self.paginate_queryset(queryset)
if page is not None:
self.current_queryset = page
serializer = self.get_serializer(page, many=True)
return self.get_paginated_response(serializer.data)
self.current_queryset = queryset
serializer = self.get_serializer(queryset, many=True)
return Response(serializer.data)
This is untested so far (not sure about functionality on Detail endpoints for instance) allows for the current_queryset to be fetched within the serializer context.
Related
What is the meaning of single model instance in RetrieveAPIView in Django REST framework.And how can we use? And will it look?
As my understanding:
single model instance: Example we use RetrieveAPIView. If we read the method that handle requests to that class, that is:
def retrieve(self, request, *args, **kwargs):
instance = self.get_object()
serializer = self.get_serializer(instance)
return Response(serializer.data)
We can see self.get_object(), it will build a Queryset to get object instance from our model class using method get(), or rather using get_object_or_404(). As we know, get() will only take 1 object instance, or it called single model instance.
Example Book.objects.get(id=10).
For more detail, we can open this link. Start from def retrieve then read also get_object().
Likewise on DestroyAPIView and UpdateAPIView.
collection of model instances: When build a Queryset, it using all() or filter(), according to what we wrote in queryset = .... or we override in def get_queryset. Example: Book.objects.all(). See this link and read def list.
CMIW.
I have a view set up to return a list of books to a user, which is retrieved from a simple book model based on the currently logged-in user. However, I also have ReadingSession model which has a foreign key relationship to both the Book, and the User.
When I'm retrieving the books for the user, I'd like to, at the very least, return a list of primary keys that I can use to get the length of in my client.
The following code will get the full set of readingsessions in my BookSerializer:
from rest_framework import serializers
from books.models import Book
class BookSerializer(serializers.ModelSerializer):
readingsession_set = serializers.PrimaryKeyRelatedField(
many=True, read_only=True)
class Meta:
model = Book
fields = ["id", "title", "author", "publisher",
"publish_date", "description", "category",
"language", "small_thumbnail", "thumbnail",
"readingsession_set"]
However, the problem with this is that it will return all of the readingsessions, regardless of whether or not the session belongs to that user.
I'd like to be able to filter that so that it will only return the readingsessions for the current user. Something along the lines of:
readingsession_set = serializers.PrimaryKeyRelatedField(queryset=ReadingSession.objects.filter(user=user), read_only=True)
But I've tried various ways of trying to pass the user (self.request.user) from the APIView but none seem to work. I've tried passing a context, and tried passing extra **kwargs in __init__ but none seem to work.
Is there a way of achieving this? Or am I taking the wrong approach?
Thanks
The user is not present on the serializer's declaration but during its instantiation.
Therefore, you can filter querysets by user within the __init__ method.
from rest_framework import serializers
from bar.models import Foo
class RandomSerializer(serializers.Serializer):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
user_foos = Foo.objects.filter(user=self._user)
self.fields['foo_ids'] = serializers.PrimaryKeyRelatedField(
required=False,
many=True,
read_only=False,
queryset=user_foos,
default=user_foos)
#property
def _user(self):
request = self.context.get('request', None)
if request:
return request.user
Don't forget to pass the request object to the serializer in the context (if necessary, e.g., using a simple APIView.
from rest_framework import views
class RandomView(views.APIView):
serializer_class = RandomSerializer
def post(self, request):
serializer = self.serializer_class(
data=request.data, context={'request': request})
# ...
serializer = RandomSerializer(data=request.data, context={'request': request}
You can access the user of the request on the serializer by means of the context.
As mentioned in the documentation, you can always do:
serializer = AccountSerializer(account, context={'request': request})
Thus, you will be able to use self.context['request'].user inside your serializer.
Hope that's what you're after.
I have a review model which has a large data so, first I do some filtration based on the date range and other things, I did it like this:
class ProgressView(generics.ListAPIView):
"""
Return a list of all Feedback reviews for progress.
"""
serializer_class = ReviewProgressSerializer
filterset_class = ProgressFilter
pagination_class = UnlimitedPagination
def get_queryset(self):
return Review.objects.filter(division__pk=self.kwargs['division_pk'])
Now, I want to do some calculations based on this filtered queryset in the serializer and return this info along with the serialized data, the problem is, I don't know how to get this queryset in the serializer or should I do it in view.
Please note that I need to do both things, serialize the review data and return the calculations too in the same response.
So, my question is how to access the queryset created by view in serializer or should I do that in another place or what.
Thank you
I figured it out, you can access your current queryset that being serialized from your serializer by self.instance
In order to have a non-readonly PrimaryKeyRelatedField, you are required to provide a queryset that contains valid options.
How can I properly populate that queryset based on the current request (user)?
The key is to subclass PrimaryKeyRelatedField and overload the get_queryset method, using the user information from the request context:
class UserFilteredPrimaryKeyRelatedField(serializers.PrimaryKeyRelatedField):
def get_queryset(self):
request = self.context.get('request', None)
queryset = super(UserFilteredPrimaryKeyRelatedField, self).get_queryset()
if not request or not queryset:
return None
return queryset.filter(user=request.user)
You can then use this new serializer just like the (unfiltered) original:
class MySerializer(serializers.ModelSerializer):
related = UserFilteredPrimaryKeyRelatedField(queryset=MyModel.objects)
Whenever the serializer accesses the queryset, it will be filtered such that only objects owned by the current user are returned.
View has a
self.request.user
attribute which you can then use to fetch user related queryset
eg
queryset = Products.objects.get(customer=self.request.user)
I am doing exactly as the example states
here is my method
class FeedViewSet(viewsets.ModelViewSet):
model = Feed
serializer_class = FullFeedSerializer
def get_queryset(self):
user = request.user
queryset = Feed.objects.get_nearby(user)
return queryset
when i execute it, it says request not defined .. which actually isn't. the example at the rest framework's site also haven't defined request. what am i doing wrong?
The request object is available (on either REST framework's class based views, or Django's standard class based views) as self.request. You're missing the self. part of that.