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Fixed #28731 -- Added an error message when using an empty Q() in a When expression.

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Otherwise it generates invalid SQL.
This commit is contained in:
Tim Martin 2017-11-05 21:34:02 +00:00 committed by Tim Graham
parent 6deaddcca3
commit 5778b5701d
2 changed files with 7 additions and 0 deletions
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2
django/db/models/expressions.py
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@ -818,6 +818,8 @@ class When(Expression):
condition, lookups = Q(**lookups), None
if condition is None or not getattr(condition, 'conditional', False) or lookups:
raise TypeError("__init__() takes either a Q object or lookups as keyword arguments")
if isinstance(condition, Q) and not condition:
raise ValueError("An empty Q() can't be used as a When() condition.")
super().__init__(output_field=None)
self.condition = condition
self.result = self._parse_expressions(then)[0]

5
tests/expressions_case/tests.py
View File

@ -1301,3 +1301,8 @@ class CaseWhenTests(SimpleTestCase):
When(condition=object())
with self.assertRaisesMessage(TypeError, msg):
When()
def test_empty_q_object(self):
msg = "An empty Q() can't be used as a When() condition."
with self.assertRaisesMessage(ValueError, msg):
When(Q(), then=Value(True))