Fixed #36065 -- Fixed ordering by expression referencing composite primary key.

Thanks Jacob Walls for the report and test and Csirmaz Bendegúz for the review.

django/db/models/expressions.py

@@ -1861,6 +1861,16 @@ class OrderBy(Expression):
         return [self.expression]
 
     def as_sql(self, compiler, connection, template=None, **extra_context):
+        if isinstance(self.expression, ColPairs):
+            sql_parts = []
+            params = []
+            for col in self.expression.get_cols():
+                copy = self.copy()
+                copy.set_source_expressions([col])
+                sql, col_params = compiler.compile(copy)
+                sql_parts.append(sql)
+                params.extend(col_params)
+            return ", ".join(sql_parts), params
         template = template or self.template
         if connection.features.supports_order_by_nulls_modifier:
             if self.nulls_last:

django/db/models/sql/compiler.py

@@ -1117,10 +1117,9 @@ class SQLCompiler:
                 )
             return results
         targets, alias, _ = self.query.trim_joins(targets, joins, path)
-        target_fields = composite.unnest(targets)
         return [
             (OrderBy(transform_function(t, alias), descending=descending), False)
-            for t in target_fields
+            for t in targets
         ]
 
     def _setup_joins(self, pieces, opts, alias):

tests/composite_pk/test_order_by.py

@@ -1,3 +1,4 @@
+from django.db.models import F
 from django.test import TestCase
 
 from .models import Comment, Tenant, User
@@ -55,3 +56,17 @@ class CompositePKOrderByTests(TestCase):
                 self.comment_1,  # (1, 1)
             ),
         )
+
+    def test_order_comments_by_pk_expr(self):
+        self.assertQuerySetEqual(
+            Comment.objects.order_by("pk"),
+            Comment.objects.order_by(F("pk")),
+        )
+        self.assertQuerySetEqual(
+            Comment.objects.order_by("-pk"),
+            Comment.objects.order_by(F("pk").desc()),
+        )
+        self.assertQuerySetEqual(
+            Comment.objects.order_by("-pk"),
+            Comment.objects.order_by(F("pk").desc(nulls_last=True)),
+        )