django ManyToMany relationship adding objects throws error - django

Question

I've a UserAnalytics object which has a one-to-one relationship with an User.
class UserAnalytics(models.Model):
user = models.ForeignKey(User, related_name='analytics', on_delete=models.CASCADE, null=True)
uptime = models.IntegerField(null=True)
feeds_viewed = models.IntegerField(null=True)
feeds_shared = models.IntegerField(null=True)
I've a Feed object which has a ManyToMany relationship with the UserAnalytics object.
class Feed(Base):
headline = models.CharField(max_length=255)
link = models.CharField(max_length=255, unique=True)
summary = models.TextField()
thumbnail = models.CharField(max_length=512, null=True)
published_date = models.DateTimeField()
views = models.IntegerField(default=0)
shares = models.IntegerField(default=0)
source = models.ForeignKey(Source, on_delete=models.CASCADE, null=True)
reader = models.ManyToManyField(User, through='Bookmark')
viewers = models.ManyToManyField(UserAnalytics)
When I try to add a feed to a UserAnalytics, using this code,
class ReadFeed(views.APIView):
def get(self, request, **kwargs):
try:
user = User.objects.get(id=kwargs.get('user_id'))
analytics = UserAnalytics.objects.get(id=user.id)
except User.DoesNotExist:
return Response({"Error": "User does not exist"}, status=status.HTTP_404_NOT_FOUND)
try:
feed = Feed.objects.get(id=kwargs.get('feed_id'))
feed.views += 1
feed.viewers.add(analytics)
feed.save()
user.analytics.add(feed)
user.analytics.save()
return Response(FeedSerializer(feed).data, status=status.HTTP_200_OK)
except Feed.DoesNotExist:
return Response({"Error": "Feed does not exist"}, status=status.HTTP_404_NOT_FOUND)
This the error that I get,
Traceback (most recent call last):
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/core/handlers/exception.py", line 35, in inner
response = get_response(request)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/core/handlers/base.py", line 128, in _get_response
response = self.process_exception_by_middleware(e, request)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/core/handlers/base.py", line 126, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/views/generic/base.py", line 69, in view
return self.dispatch(request, *args, **kwargs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/rest_framework/views.py", line 494, in dispatch
response = self.handle_exception(exc)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/rest_framework/views.py", line 454, in handle_exception
self.raise_uncaught_exception(exc)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/rest_framework/views.py", line 491, in dispatch
response = handler(request, *args, **kwargs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/aggregator/api.py", line 28, in get
feed.viewers.add(user.analytics)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 898, in add
self._add_items(self.source_field_name, self.target_field_name, *objs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/fields/related_descriptors.py", line 1045, in _add_items
'%s__in' % target_field_name: new_ids,
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/query.py", line 836, in filter
return self._filter_or_exclude(False, *args, **kwargs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/query.py", line 854, in _filter_or_exclude
clone.query.add_q(Q(*args, **kwargs))
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/sql/query.py", line 1253, in add_q
clause, _ = self._add_q(q_object, self.used_aliases)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/sql/query.py", line 1277, in _add_q
split_subq=split_subq,
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/sql/query.py", line 1215, in build_filter
condition = self.build_lookup(lookups, col, value)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/sql/query.py", line 1085, in build_lookup
lookup = lookup_class(lhs, rhs)
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/lookups.py", line 18, in __init__
self.rhs = self.get_prep_lookup()
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/fields/related_lookups.py", line 59, in get_prep_lookup
self.rhs = [target_field.get_prep_value(v) for v in self.rhs]
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/fields/related_lookups.py", line 59, in <listcomp>
self.rhs = [target_field.get_prep_value(v) for v in self.rhs]
File "/Users/mstewart/Dropbox/xdrive/ftb/ftb_core_backend/env/lib/python3.6/site-packages/django/db/models/fields/__init__.py", line 947, in get_prep_value
return int(value)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'RelatedManager'
[28/May/2018 15:55:19] "GET /api/v1/aggregator/read/4/67 HTTP/1.1" 500 18150
TypeError: int() argument must be a string, a bytes-like object or a number, not 'RelatedManager'
What am I doing wrong here?

Answer 1

I think you have edited the error out of your view.
The traceback shows that your file api.py:28 has a line:
feed.viewers.add(user.analytics)
But user.analytics is a one-to-many relation, and thus one user can have several UserAnalytics objects (since many of these can all refer to the same use). As a result user.analytics is not a single object, nor a collection, but a RelatedManager: some sort of manager to manage the related objects.
You can add .all() and perform iterable unpacking to add all the .analytics objects with a single call:
feed.viewers.add(*user.analytics.all())
(notice the asterisk * in the call).
In case every user has at most one UserAnalytics object, you better use a OneToOneField, so:
# only in case a user has *at most* one UserAnalytics object
class UserAnalytics(models.Model):
user = models.OneToOneField(User, related_name='analytics', on_delete=models.CASCADE, null=True)
uptime = models.IntegerField(null=True)
feeds_viewed = models.IntegerField(null=True)
feeds_shared = models.IntegerField(null=True)
In that case a user.analyics will either return the associated UserAnalytics object (given there is one), or - if there is no such object - raise a UserAnalytics.DoesNotExist error.