I have the following two models:
Class Foo(models.model):
param1 = ...
param2 = ...
...
paramN = ...
Class Bar(models.model):
foo = models.ForeignKey(Foo)
...
...
GOAL: Compute a QuerySet of all instances of Foo such that more than 1 Bar instance is connected to it
I have been looking for a solution and this seems to work for everybody else
Foo.objects.annotate(num_bar=Count('bar')).filter(num_bar__gt=1)
This gave me a FieldError
saying that 'bar'
was not a possible field for Foo
, I then tried 'bar_set'
and also got the same error
Is there a chance I am implementing them wrong, or because they are old they are depreciated now? Any help would be appreciated!
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/manager.py", line 127, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/query.py", line 794, in annotate
obj.query.add_annotation(annotation, alias, is_summary=False)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 982, in add_annotation
summarize=is_summary)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/aggregates.py", line 20, in resolve_expression
c = super(Aggregate, self).resolve_expression(query, allow_joins, reuse, summarize)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 491, in resolve_expression
c.source_expressions[pos] = arg.resolve_expression(query, allow_joins, reuse, summarize, for_save)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 448, in resolve_expression
return query.resolve_ref(self.name, allow_joins, reuse, summarize)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1532, in resolve_ref
self.get_initial_alias(), reuse)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1471, in setup_joins
names, opts, allow_many, fail_on_missing=True)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1396, in names_to_path
"Choices are: %s" % (name, ", ".join(available)))
FieldError: Cannot resolve keyword 'bar' into field. Choices are: param1, param2, param3, ..., paramN
my django version is 1.8.3
There can be multiple reasons for this error, I'll try to tell the probable causes:
num_model
. also check if you can get the count of them ( the dirty way :) ):
for foo in Foo.objects.all(): if foo.bar_set.count() < 2: #do sth like : foo.bar_set.get() or temp = temp + 1
as of your short description of model (not your main code), cannot find other causes. Your query should work.
So after trying a lot, this was a solution that worked:
Bar.objects.values("foo_id").annotate(Count("foo_id")).filter(pk__count__gt=1)
Not exactly sure why this worked and the other didn't, but it essentially just gets the count of Bar
objects with the same foo_id
and makes sure there is more than 1.
If somebody would like to explain a potential reason why this works and the other did not, that would be appreciated.
I had the same issue by import mistake. This is solution for my use case
# from django.db.models.sql.aggregates import Count # wrong import
from django.db.models import Count # correct one
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