Fixed #21554 -- Incorrect SQL generated when using multiple inheritance.

django/db/models/sql/compiler.py

@@ -284,25 +284,32 @@ class SQLCompiler(object):
                 continue
             alias = self.query.join_parent_model(opts, model, start_alias,
                                                  seen_models)
+            column = field.column
+            for seen_model, seen_alias in seen_models.items():
+                if seen_model and seen_alias == alias:
+                    ancestor_link = seen_model._meta.get_ancestor_link(model)
+                    if ancestor_link:
+                        column = ancestor_link.column
+                    break
             table = self.query.alias_map[alias].table_name
-            if table in only_load and field.column not in only_load[table]:
+            if table in only_load and column not in only_load[table]:
                 continue
             if as_pairs:
-                result.append((alias, field.column))
+                result.append((alias, column))
                 aliases.add(alias)
                 continue
-            if with_aliases and field.column in col_aliases:
+            if with_aliases and column in col_aliases:
                 c_alias = 'Col%d' % len(col_aliases)
                 result.append('%s.%s AS %s' % (qn(alias),
-                    qn2(field.column), c_alias))
+                    qn2(column), c_alias))
                 col_aliases.add(c_alias)
                 aliases.add(c_alias)
             else:
-                r = '%s.%s' % (qn(alias), qn2(field.column))
+                r = '%s.%s' % (qn(alias), qn2(column))
                 result.append(r)
                 aliases.add(r)
                 if with_aliases:
-                    col_aliases.add(field.column)
+                    col_aliases.add(column)
         return result, aliases
 
     def get_distinct(self):

tests/model_inheritance_regress/models.py

@@ -233,3 +233,17 @@ class User(models.Model):
 class Profile(User):
     profile_id = models.AutoField(primary_key=True)
     extra = models.CharField(max_length=30, blank=True)
+
+
+# Check concrete + concrete -> concrete -> concrete
+class Politician(models.Model):
+    politician_id = models.AutoField(primary_key=True)
+    title = models.CharField(max_length=50)
+
+
+class Congressman(Person, Politician):
+    state = models.CharField(max_length=2)
+
+
+class Senator(Congressman):
+    pass

tests/model_inheritance_regress/tests.py

@@ -15,7 +15,7 @@ from .models import (Place, Restaurant, ItalianRestaurant, ParkingLot,
     SelfRefChild, ArticleWithAuthor, M2MChild, QualityControl, DerivedM,
     Person, BirthdayParty, BachelorParty, MessyBachelorParty,
     InternalCertificationAudit, BusStation, TrainStation, User, Profile,
-    ParkingLot4A, ParkingLot4B)
+    ParkingLot4A, ParkingLot4B, Senator)
 
 
 class ModelInheritanceTest(TestCase):
@@ -455,3 +455,10 @@ class ModelInheritanceTest(TestCase):
         # used in the qs and top contains direct pointer to the bottom model.
         qs = ItalianRestaurant.objects.values_list('serves_gnocchi').filter(name='foo')
         self.assertEqual(str(qs.query).count('JOIN'), 1)
+
+    def test_issue_21554(self):
+        senator = Senator.objects.create(
+            name='John Doe', title='X', state='Y'
+        )
+
+        Senator.objects.get(pk=senator.pk)