I want to be able to list the items that either a user has added (they are listed as the creator) or the item has been approved.
So I basically need to select:
item.creator = owner or item.moderated = False
How would I do this in Django? (preferably with a filter or queryset).
This question is related to
django
django-queryset
It is worth to note that it's possible to add Q expressions.
For example:
from django.db.models import Q
query = Q(first_name='mark')
query.add(Q(email='[email protected]'), Q.OR)
query.add(Q(last_name='doe'), Q.AND)
queryset = User.objects.filter(query)
This ends up with a query like :
(first_name = 'mark' or email = '[email protected]') and last_name = 'doe'
This way there is no need to deal with or operators, reduce's etc.
You can use the | operator to combine querysets directly without needing Q objects:
result = Item.objects.filter(item.creator = owner) | Item.objects.filter(item.moderated = False)
(edit - I was initially unsure if this caused an extra query but @spookylukey pointed out that lazy queryset evaluation takes care of that)
You want to make filter dynamic then you have to use Lambda like
from django.db.models import Q
brands = ['ABC','DEF' , 'GHI']
queryset = Product.objects.filter(reduce(lambda x, y: x | y, [Q(brand=item) for item in brands]))
reduce(lambda x, y: x | y, [Q(brand=item) for item in brands]) is equivalent to
Q(brand=brands[0]) | Q(brand=brands[1]) | Q(brand=brands[2]) | .....
Similar to older answers, but a bit simpler, without the lambda:
filter_kwargs = {
'field_a': 123,
'field_b__in': (3, 4, 5, ),
}
To filter these two conditions using OR:
Item.objects.filter(Q(field_a=123) | Q(field_b__in=(3, 4, 5, ))
To get the same result programmatically:
list_of_Q = [Q(**{key: val}) for key, val in filter_kwargs.items()]
Item.objects.filter(reduce(operator.or_, list_of_Q))
(broken in two lines here, for clarity)
operator is in standard library: import operator
From docstring:
or_(a, b) -- Same as a | b.
For Python3, reduce is not a builtin any more but is still in the standard library: from functools import reduce
P.S.
Don't forget to make sure list_of_Q is not empty - reduce() will choke on empty list, it needs at least one element.
This might be useful https://docs.djangoproject.com/en/dev/topics/db/queries/#spanning-multi-valued-relationships
Basically it sounds like they act as OR
Source: Stackoverflow.com