Prefixing Q Objects

[Robert Schindler]

I'm currently spending a lot of time on development of a project using Django and worked out something that I think could be of use for all Django users.

I added a new .prefix(prefix) method to the Q object, allowing to shift pre-built q objects to a related field. I think this can change the way people build managers completely, because instead of methods returning filtered querysets, one can just return Q objects, which can then be used from related models without repeating the filtering logic.

This is the simple implementation.

`
class Q(django.db.models.Q):

"""
A custom Q implementation that allows prefixing existing Q objects with some
related field name dynamically.
"""

def prefix(self, prefix):

"""Recursively copies the Q object, prefixing all lookup keys.

The prefix and the existing filter key are delimited by the lookup separator .
Use this feature to delegate existing query constraints to a related field.
"""
return type(self)(

*(

child.prefix(prefix)
if isinstance(child, Q)
else (prefix + LOOKUP_SEP + child[0], child[1])
for child in self.children

),
_connector=self.connector,
_negated=self.negated,

)

`

What do you think, is it worth creating a PR for this functionality? I haven't written the docs yet, but could write something if you like the addition.

Best regards
Robert