Fixed #35275 -- Fixed Meta.constraints validation crash on UniqueConstraint with OpClass().

This also introduces Expression.constraint_validation_compatible that
allows specifying that expression should be ignored during a constraint
validation.

2 files changed, 5 insertions, 7 deletions

diff --git a/django/contrib/postgres/constraints.py b/django/contrib/postgres/constraints.py
index ff702c53b0..a31f657183 100644
--- a/django/contrib/postgres/constraints.py
+++ b/django/contrib/postgres/constraints.py
@@ -1,6 +1,5 @@
 from types import NoneType
 
-from django.contrib.postgres.indexes import OpClass
 from django.core.exceptions import ValidationError
 from django.db import DEFAULT_DB_ALIAS, NotSupportedError
 from django.db.backends.ddl_references import Expressions, Statement, Table
@@ -208,12 +207,10 @@ class ExclusionConstraint(BaseConstraint):
                         if isinstance(expr, F) and expr.name in exclude:
                             return
             rhs_expression = expression.replace_expressions(replacements)
-            # Remove OpClass because it only has sense during the constraint
-            # creation.
-            if isinstance(expression, OpClass):
-                expression = expression.get_source_expressions()[0]
-            if isinstance(rhs_expression, OpClass):
-                rhs_expression = rhs_expression.get_source_expressions()[0]
+            if hasattr(expression, "get_expression_for_validation"):
+                expression = expression.get_expression_for_validation()
+            if hasattr(rhs_expression, "get_expression_for_validation"):
+                rhs_expression = rhs_expression.get_expression_for_validation()
             lookup = PostgresOperatorLookup(lhs=expression, rhs=rhs_expression)
             lookup.postgres_operator = operator
             lookups.append(lookup)
diff --git a/django/contrib/postgres/indexes.py b/django/contrib/postgres/indexes.py
index cc944ed335..05fdbeed5e 100644
--- a/django/contrib/postgres/indexes.py
+++ b/django/contrib/postgres/indexes.py
@@ -244,6 +244,7 @@ class SpGistIndex(PostgresIndex):
 
 class OpClass(Func):
     template = "%(expressions)s %(name)s"
+    constraint_validation_compatible = False
 
     def __init__(self, expression, name):
         super().__init__(expression, name=name)