id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34871	Validation of UniqueConstraint with Case() crashes.	Andrew Roberts	Simon Charette	"Consider the following model where we want to guarantee that there is only one active profile per email address:

{{{
class Profile(models.Model):
    active = models.BooleanField()
    email = models.CharField(max_length=255)

    class Meta:
        constraints = [
            models.UniqueConstraint(
                Case(When(active=True, then=F(""email""))),
                name=""unique_active_email"",
            )
        ]
        app_label = ""test""
}}}

Model validation indirectly calls constraint.validate(), but to simulate this we can execute:

{{{
constraint = Profile._meta.constraints[0]
constraint.validate(Profile, Profile(active=True, email=""test@example.com""))
}}}

This fails with:
{{{
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[21], line 1
----> 1 constraint.validate(Profile, Profile(active=True, email=""test@example.com""))

File /usr/local/lib/python3.11/site-packages/django/db/models/constraints.py:346, in UniqueConstraint.validate(self, model, instance, exclude, using)
    344         if isinstance(expr, OrderBy):
    345             expr = expr.expression
--> 346         expressions.append(Exact(expr, expr.replace_expressions(replacements)))
    347     queryset = queryset.filter(*expressions)
    348 model_class_pk = instance._get_pk_val(model._meta)

File /usr/local/lib/python3.11/site-packages/django/db/models/expressions.py:401, in BaseExpression.replace_expressions(self, replacements)
    398 clone = self.copy()
    399 source_expressions = clone.get_source_expressions()
    400 clone.set_source_expressions(
--> 401     [
    402         expr.replace_expressions(replacements) if expr else None
    403         for expr in source_expressions
    404     ]
    405 )
    406 return clone

File /usr/local/lib/python3.11/site-packages/django/db/models/expressions.py:402, in <listcomp>(.0)
    398 clone = self.copy()
    399 source_expressions = clone.get_source_expressions()
    400 clone.set_source_expressions(
    401     [
--> 402         expr.replace_expressions(replacements) if expr else None
    403         for expr in source_expressions
    404     ]
    405 )
    406 return clone

File /usr/local/lib/python3.11/site-packages/django/db/models/expressions.py:401, in BaseExpression.replace_expressions(self, replacements)
    398 clone = self.copy()
    399 source_expressions = clone.get_source_expressions()
    400 clone.set_source_expressions(
--> 401     [
    402         expr.replace_expressions(replacements) if expr else None
    403         for expr in source_expressions
    404     ]
    405 )
    406 return clone

File /usr/local/lib/python3.11/site-packages/django/db/models/expressions.py:402, in <listcomp>(.0)
    398 clone = self.copy()
    399 source_expressions = clone.get_source_expressions()
    400 clone.set_source_expressions(
    401     [
--> 402         expr.replace_expressions(replacements) if expr else None
    403         for expr in source_expressions
    404     ]
    405 )
    406 return clone

AttributeError: 'Q' object has no attribute 'replace_expressions'
}}}
"	Bug	closed	Database layer (models, ORM)	4.2	Normal	fixed		Gagaro Simon Charette Václav Řehák Mark Gensler	Ready for checkin	1	0	0	0	0	0