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[1.8.x] Fixed #24508 -- Made annotations commutative 

Backport of 127b3873d0 from master
This commit is contained in:
Josh Smeaton 2015-03-20 15:47:43 +11:00
parent dc2cff5fcb
commit 3a1886d111
2 changed files with 20 additions and 2 deletions
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14
django/db/models/expressions.py
View File

@ -238,7 +238,16 @@ class BaseExpression(object):
""" """
Attempts to infer the output type of the expression. If the output Attempts to infer the output type of the expression. If the output
fields of all source fields match then we can simply infer the same fields of all source fields match then we can simply infer the same
type here. type here. This isn't always correct, but it makes sense most of the
time.
Consider the difference between `2 + 2` and `2 / 3`. Inferring
the type here is a convenience for the common case. The user should
supply their own output_field with more complex computations.
If a source does not have an `_output_field` then we exclude it from
this check. If all sources are `None`, then an error will be thrown
higher up the stack in the `output_field` property.
""" """
if self._output_field is None: if self._output_field is None:
sources = self.get_source_fields() sources = self.get_source_fields()
@ -246,8 +255,9 @@ class BaseExpression(object):
if num_sources == 0: if num_sources == 0:
self._output_field = None self._output_field = None
else: else:
self._output_field = sources[0]
for source in sources: for source in sources:
if self._output_field is None:
self._output_field = source
if source is not None and not isinstance(self._output_field, source.__class__): if source is not None and not isinstance(self._output_field, source.__class__):
raise FieldError( raise FieldError(
"Expression contains mixed types. You must set output_field") "Expression contains mixed types. You must set output_field")

8
tests/annotations/tests.py
View File

@ -99,6 +99,14 @@ class NonAggregateAnnotationTestCase(TestCase):
sum_rating=Sum('rating') sum_rating=Sum('rating')
).filter(sum_rating=F('nope'))) ).filter(sum_rating=F('nope')))
def test_combined_annotation_commutative(self):
book1 = Book.objects.annotate(adjusted_rating=F('rating') + 2).get(pk=self.b1.pk)
book2 = Book.objects.annotate(adjusted_rating=2 + F('rating')).get(pk=self.b1.pk)
self.assertEqual(book1.adjusted_rating, book2.adjusted_rating)
book1 = Book.objects.annotate(adjusted_rating=F('rating') + None).get(pk=self.b1.pk)
book2 = Book.objects.annotate(adjusted_rating=None + F('rating')).get(pk=self.b1.pk)
self.assertEqual(book1.adjusted_rating, book2.adjusted_rating)
def test_update_with_annotation(self): def test_update_with_annotation(self):
book_preupdate = Book.objects.get(pk=2) book_preupdate = Book.objects.get(pk=2)
Book.objects.annotate(other_rating=F('rating') - 1).update(rating=F('other_rating')) Book.objects.annotate(other_rating=F('rating') - 1).update(rating=F('other_rating'))