I have a model in which I was trying to get a count for records that
matched three variable values and found an interesting edge case not in the
documents
for conditional expressions
<https://docs.djangoproject.com/en/1.11/ref/models/conditional-expressions/#when>.
Specifically, if you have to use a Q expression for a not query, you can't
mix them with lookups.
This is all on Django 1.8 with python 2.7.12
for example,
SomeModel.objects.aggregate(total = Count(Case(When(~Q(some_field__icontains
= 'value'), field_two = 2, field_three = True, then = 1), output_field =
IntegerField()))
will result in a TypeError
/home/jason/.virtualenvs/work/lib/python2.7/site-packages/django/db/models/expressions.pyc
in __init__(self, condition, then, **lookups)
687 condition, lookups = Q(**lookups), None
688 if condition is None or not isinstance(condition, Q) or
lookups:
--> 689 raise TypeError("__init__() takes either a Q object or
lookups as keyword arguments")
690 super(When, self).__init__(output_field=None)
691 self.condition = condition
TypeError: __init__() takes either a Q object or lookups as keyword
arguments
However, moving the original to a full ANDed Q expression like
query = ~Q(some_field__icontains = 'value') & Q(field_two = 2) & Q(field_three
= True)
SomeModel.objects.aggregate(total = Count(Case(When(query, then = 1),
output_field = IntegerField()))
works fine. I couldn't find anything specifically about this in the docs,
so is this explicit behavior or an undocumented issue?
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