[3.1.x] Fixed #31735 -- Fixed migrations crash on namespaced inline FK addition on PostgreSQL.

The namespace of the constraint must be included when making the
constraint immediate.

Regression in 22ce5d0031bd795ade081394043833e82046016c.

Thanks Rodrigo Estevao for the report.

Backport of 2e8941b6f90e65ffad3f07083b8de59e8ed29767 from master

4 files changed, 36 insertions, 1 deletions

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index 2b2ad9cdb4..e0bf731d8a 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -466,8 +466,10 @@ class BaseDatabaseSchemaEditor:
             if self.sql_create_column_inline_fk:
                 to_table = field.remote_field.model._meta.db_table
                 to_column = field.remote_field.model._meta.get_field(field.remote_field.field_name).column
+                namespace, _ = split_identifier(model._meta.db_table)
                 definition += " " + self.sql_create_column_inline_fk % {
                     'name': self._fk_constraint_name(model, field, constraint_suffix),
+                    'namespace': '%s.' % self.quote_name(namespace) if namespace else '',
                     'column': self.quote_name(field.column),
                     'to_table': self.quote_name(to_table),
                     'to_column': self.quote_name(to_column),
diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index e5a0008025..d12ef35073 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -23,7 +23,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     # transaction.
     sql_create_column_inline_fk = (
         'CONSTRAINT %(name)s REFERENCES %(to_table)s(%(to_column)s)%(deferrable)s'
-        '; SET CONSTRAINTS %(name)s IMMEDIATE'
+        '; SET CONSTRAINTS %(namespace)s%(name)s IMMEDIATE'
     )
     # Setting the constraint to IMMEDIATE runs any deferred checks to allow
     # dropping it in the same transaction.
diff --git a/docs/releases/3.0.8.txt b/docs/releases/3.0.8.txt
index 6bb3e39de7..f23208f9ae 100644
--- a/docs/releases/3.0.8.txt
+++ b/docs/releases/3.0.8.txt
@@ -18,3 +18,7 @@ Bugfixes
 * Reallowed, following a regression in Django 3.0, non-expressions having a
   ``filterable`` attribute to be used as the right-hand side in queryset
   filters (:ticket:`31664`).
+
+* Fixed a regression in Django 3.0.2 that caused a migration crash on
+  PostgreSQL when adding a foreign key to a model with a namespaced
+  ``db_table`` (:ticket:`31735`).
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 9aa1e239ac..59fe66953d 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -3059,6 +3059,35 @@ class SchemaTests(TransactionTestCase):
         student = Student.objects.create(name='Some man')
         doc.students.add(student)
 
+    @isolate_apps('schema')
+    @unittest.skipUnless(connection.vendor == 'postgresql', 'PostgreSQL specific db_table syntax.')
+    def test_namespaced_db_table_foreign_key_reference(self):
+        with connection.cursor() as cursor:
+            cursor.execute('CREATE SCHEMA django_schema_tests')
+
+        def delete_schema():
+            with connection.cursor() as cursor:
+                cursor.execute('DROP SCHEMA django_schema_tests CASCADE')
+
+        self.addCleanup(delete_schema)
+
+        class Author(Model):
+            class Meta:
+                app_label = 'schema'
+
+        class Book(Model):
+            class Meta:
+                app_label = 'schema'
+                db_table = '"django_schema_tests"."schema_book"'
+
+        author = ForeignKey(Author, CASCADE)
+        author.set_attributes_from_name('author')
+
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+            editor.create_model(Book)
+            editor.add_field(Book, author)
+
     def test_rename_table_renames_deferred_sql_references(self):
         atomic_rename = connection.features.supports_atomic_references_rename
         with connection.schema_editor(atomic=atomic_rename) as editor: