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Fixed #29195 -- Fixed Exists.output_field resolution on single-valued queries.

Browse source 
The Subquery class which Exists inherits from defaulted to using single-valued
querie's field if no output_field was explicitly specified on initialization
which was bypassing the Exists.output_field defined at the class level.

Moving Subquery's dynamic output_field resolution to _resolve_output_field
should make sure the fallback logic is only performed if required.

Regression in 08654a99bb.

Thanks Oli Warner for the detailed report.
This commit is contained in:
Simon Charette 2018-03-08 02:06:19 -05:00 • committed by Tim Graham
parent fd9398816e
commit 277ed07209
3 changed files with 11 additions and 3 deletions
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7
django/db/models/expressions.py
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@ -960,10 +960,13 @@ class Subquery(Expression):
def __init__(self, queryset, output_field=None, **extra):
self.queryset = queryset
self.extra = extra
if output_field is None and len(self.queryset.query.select) == 1:
output_field = self.queryset.query.select[0].field
super().__init__(output_field)
def _resolve_output_field(self):
if len(self.queryset.query.select) == 1:
return self.queryset.query.select[0].field
return super()._resolve_output_field()
def copy(self):
clone = super().copy()
clone.queryset = clone.queryset.all()