Commit eeb10d5f authored by Luke Plant's avatar Luke Plant
Browse files

Optimised use of 'in' operator on QuerySet using an explicit __contains__ method. 

Without this change, use of 'in' on a QuerySet resulted in ._result_cache
being fully populated, which sometimes is unnecessary work.



git-svn-id: http://code.djangoproject.com/svn/django/trunk@11803 bcc190cf-cafb-0310-a4f2-bffc1f526a37
parent bb428f3e

django/db/models/query.py

+30 −0
Original line number Diff line number Diff line
@@ -107,6 +107,36 @@ class QuerySet(object): 
            return False

        return True



    def __contains__(self, val):

        # The 'in' operator works without this method, due to __iter__. This

        # implementation exists only to shortcut the creation of Model

        # instances, by bailing out early if we find a matching element.

        pos = 0

        if self._result_cache is not None:

            if val in self._result_cache:

                return True

            elif self._iter is None:

                # iterator is exhausted, so we have our answer

                return False

            # remember not to check these again:

            pos = len(self._result_cache)

        else:

            # We need to start filling the result cache out. The following

            # ensures that self._iter is not None and self._result_cache is not

            # None

            it = iter(self)



        # Carry on, one result at a time.

        while True:

            if len(self._result_cache) <= pos:

                self._fill_cache(num=1)

            if self._iter is None:

                # we ran out of items

                return False

            if self._result_cache[pos] == val:

                return True

            pos += 1



    def __getitem__(self, k):

        """

        Retrieves an item or slice from the set of results.

tests/modeltests/basic/models.py

+8 −0
Original line number Diff line number Diff line
@@ -211,6 +211,14 @@ True 
>>> Article.objects.get(id__exact=8) == Article.objects.get(id__exact=7)

False



# You can use 'in' to test for membership...

>>> a8 in Article.objects.all()

True



# ... but there will often be more efficient ways if that is all you need:

>>> Article.objects.filter(id=a8.id).exists()

True



# dates() returns a list of available dates of the given scope for the given field.

>>> Article.objects.dates('pub_date', 'year')

[datetime.datetime(2005, 1, 1, 0, 0)]