I had a similar case and found that, using boolean logic to put the negations on the leaves of the tree solved the issue.
I made a Django snippet here :
https://djangosnippets.org/snippets/10866/
Here is a copy of my code :
def put_Q_negations_to_leaves(
query_filter: Q,
negate: bool = False,
first_call: bool = True,
debug: bool = False,
):
negate_below = (negate != query_filter.negated) # XOR
if debug:
logger.info(
f"put_Q_negations_to_leaves() query_filter:{query_filter}"
f" negate:{negate} negate_below:{negate_below}"
)
true_kwargs = {
"_connector": query_filter.connector,
"_negated": False,
}
new_children = []
for child in query_filter.children:
if debug:
logger.info(child.__repr__())
if not isinstance(child, Q):
if negate_below:
new_child = ~Q(child)
else:
new_child = child
else:
new_child = put_Q_negations_to_leaves(child, negate=negate_below, first_call=False)
if debug:
logger.info(new_child.__repr__())
new_children.append(new_child)
if len(new_children) == 1:
# One child
if isinstance(new_children[0], Q) or first_call == False:
# Double negation canceled out if possible
return new_children[0]
else:
true_kwargs["_negated"] = negate_below
if negate_below:
if true_kwargs["_connector"] == Q.AND:
true_kwargs["_connector"] = Q.OR
else:
true_kwargs["_connector"] = Q.AND
return Q(*new_children, **true_kwargs)
To make this snippet works in all cases, it is necessary to change the following lines :
if negate_below:
new_child = ~Q(child)
You must handle all negation of field lookups :
https://docs.djangoproject.com/en/4.0/ref/models/querysets/#field-lookups-1
with string manipulation on the first element of the tuple.
For that, you can look at this answer on StackOverflow : How do I do a not equal in Django queryset filtering? https://stackoverflow.com/a/29227603/5796086
However, for most uses, it will be simpler to use a SubQuery (or Exists).
Use example :
from django.db.models import Q, F
# For simplicity, and avoiding mixing args and kwargs, we only use args since :
# ("some_fk__some_other_fk__some_field", 111) arg
# is equivalent to
# some_fk__some_other_fk__some_field=111 kwarg
unmodified_filter = ~Q(
("some_fk__some_other_fk__some_field", 111),
Q(("some_fk__some_other_fk__some_other_field__lt", 11))
| ~Q(("some_fk__some_other_fk__some_yet_another_field", F("some_fk__some_yet_another_field")))
)
modified_filter = put_Q_negations_to_leaves(unmodified_filter)
print(unmodified_filter)
print(modified_filter)
This will output something that you can beautify like this:
Before:
(NOT
(AND:
('some_fk__some_other_fk__some_field', 111),
(OR:
('some_fk__some_other_fk__some_other_field__lt', 11),
(NOT
(AND: ('some_fk__some_other_fk__some_yet_another_field', F(some_fk__some_yet_another_field)))
)
)
)
)
After:
(OR:
(NOT
(AND: ('some_fk__some_other_fk__some_field', 111))
),
(AND:
(NOT
(AND: ('some_fk__some_other_fk__some_other_field__lt', 11))
), <-- This is where negation of lookups like "lt" -> "gte" should be handled
('some_fk__some_other_fk__some_yet_another_field', F(some_fk__some_yet_another_field)) <-- Double negation canceled out
)
)
