Fixed #23009: Shorten FK identifiers in add_field and make consistent

django/db/backends/schema.py

@@ -435,11 +435,7 @@ class BaseDatabaseSchemaEditor(object):
             to_column = field.rel.to._meta.get_field(field.rel.field_name).column
             self.deferred_sql.append(
                 self.sql_create_fk % {
-                    "name": self.quote_name('%s_refs_%s_%x' % (
-                        field.column,
-                        to_column,
-                        abs(hash((model._meta.db_table, to_table)))
-                    )),
+                    "name": self._create_index_name(model, [field.column], suffix="_fk_%s_%s" % (to_table, to_column)),
                     "table": self.quote_name(model._meta.db_table),
                     "column": self.quote_name(field.column),
                     "to_table": self.quote_name(to_table),
@@ -737,13 +733,15 @@ class BaseDatabaseSchemaEditor(object):
             )
         # Does it have a foreign key?
         if new_field.rel:
+            to_table = new_field.rel.to._meta.db_table
+            to_column = new_field.rel.get_related_field().column
             self.execute(
                 self.sql_create_fk % {
                     "table": self.quote_name(model._meta.db_table),
-                    "name": self._create_index_name(model, [new_field.column], suffix="_fk"),
+                    "name": self._create_index_name(model, [new_field.column], suffix="_fk_%s_%s" % (to_table, to_column)),
                     "column": self.quote_name(new_field.column),
-                    "to_table": self.quote_name(new_field.rel.to._meta.db_table),
-                    "to_column": self.quote_name(new_field.rel.get_related_field().column),
+                    "to_table": self.quote_name(to_table),
+                    "to_column": self.quote_name(to_column),
                 }
             )
         # Rebuild FKs that pointed to us if we previously had to drop them

tests/schema/models.py

@@ -129,8 +129,16 @@ class UniqueTest(models.Model):
         unique_together = ["year", "slug"]
 
 
+class AuthorWithEvenLongerName(models.Model):
+    name = models.CharField(max_length=255)
+    height = models.PositiveIntegerField(null=True, blank=True)
+
+    class Meta:
+        apps = new_apps
+
+
 class BookWithLongName(models.Model):
-    author_foreign_key_with_really_long_field_name = models.ForeignKey(Author)
+    author_foreign_key_with_really_long_field_name = models.ForeignKey(AuthorWithEvenLongerName)
 
     class Meta:
         apps = new_apps

tests/schema/tests.py

@@ -9,7 +9,8 @@ from django.db.models.fields.related import ManyToManyField, ForeignKey
 from django.db.transaction import atomic
 from .models import (Author, AuthorWithM2M, Book, BookWithLongName,
     BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename,
-    UniqueTest, Thing, TagThrough, BookWithM2MThrough, AuthorTag, AuthorWithM2MThrough)
+    UniqueTest, Thing, TagThrough, BookWithM2MThrough, AuthorTag, AuthorWithM2MThrough,
+    AuthorWithEvenLongerName)
 
 
 class SchemaTests(TransactionTestCase):
@@ -26,7 +27,7 @@ class SchemaTests(TransactionTestCase):
     models = [
         Author, AuthorWithM2M, Book, BookWithLongName, BookWithSlug,
         BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename, UniqueTest,
-        Thing, TagThrough, BookWithM2MThrough
+        Thing, TagThrough, BookWithM2MThrough, AuthorWithEvenLongerName
     ]
 
     # Utility functions
@@ -846,14 +847,15 @@ class SchemaTests(TransactionTestCase):
         except SomeError:
             self.assertFalse(connection.in_atomic_block)
 
+    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
     def test_foreign_key_index_long_names_regression(self):
         """
-        Regression test for #21497. Only affects databases that supports
-        foreign keys.
+        Regression test for #21497.
+        Only affects databases that supports foreign keys.
         """
         # Create the table
         with connection.schema_editor() as editor:
-            editor.create_model(Author)
+            editor.create_model(AuthorWithEvenLongerName)
             editor.create_model(BookWithLongName)
         # Find the properly shortened column name
         column_name = connection.ops.quote_name("author_foreign_key_with_really_long_field_name_id")
@@ -864,6 +866,25 @@ class SchemaTests(TransactionTestCase):
             self.get_indexes(BookWithLongName._meta.db_table),
         )
 
+    @unittest.skipUnless(connection.features.supports_foreign_keys, "No FK support")
+    def test_add_foreign_key_long_names(self):
+        """
+        Regression test for #23009.
+        Only affects databases that supports foreign keys.
+        """
+        # Create the initial tables
+        with connection.schema_editor() as editor:
+            editor.create_model(AuthorWithEvenLongerName)
+            editor.create_model(BookWithLongName)
+        # Add a second FK, this would fail due to long ref name before the fix
+        new_field = ForeignKey(AuthorWithEvenLongerName, related_name="something")
+        new_field.set_attributes_from_name("author_other_really_long_named_i_mean_so_long_fk")
+        with connection.schema_editor() as editor:
+            editor.add_field(
+                BookWithLongName,
+                new_field,
+            )
+
     def test_creation_deletion_reserved_names(self):
         """
         Tries creating a model's table, and then deleting it when it has a