From b1cbbe926789bcfc2e118c7d7c7a0f30fab5248a Mon Sep 17 00:00:00 2001
From: Simon Charette <charette.s@gmail.com>
Date: Tue, 24 May 2016 15:38:01 -0400
Subject: [PATCH] Refs #25530 -- Deleted deferred SQL references on delete
 operation.

---
 django/db/backends/base/schema.py    |  8 ++++++++
 django/db/backends/sqlite3/schema.py |  9 ++++-----
 tests/schema/tests.py                | 22 +++++++++++++++++-----
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index e31251ae81..91ee3dac22 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -314,6 +314,10 @@ class BaseDatabaseSchemaEditor:
         self.execute(self.sql_delete_table % {
             "table": self.quote_name(model._meta.db_table),
         })
+        # Remove all deferred statements referencing the deleted table.
+        for sql in list(self.deferred_sql):
+            if isinstance(sql, Statement) and sql.references_table(model._meta.db_table):
+                self.deferred_sql.remove(sql)
 
     def add_index(self, model, index):
         """Add an index on a model."""
@@ -456,6 +460,10 @@ class BaseDatabaseSchemaEditor:
         # Reset connection if required
         if self.connection.features.connection_persists_old_columns:
             self.connection.close()
+        # Remove all deferred statements referencing the deleted table.
+        for sql in list(self.deferred_sql):
+            if isinstance(sql, Statement) and sql.references_column(model._meta.db_table, field.column):
+                self.deferred_sql.remove(sql)
 
     def alter_field(self, model, old_field, new_field, strict=False):
         """
diff --git a/django/db/backends/sqlite3/schema.py b/django/db/backends/sqlite3/schema.py
index 5517d78a97..3bf71e071a 100644
--- a/django/db/backends/sqlite3/schema.py
+++ b/django/db/backends/sqlite3/schema.py
@@ -190,11 +190,6 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             # Rename the old table to make way for the new
             self.alter_db_table(model, temp_model._meta.db_table, model._meta.db_table)
 
-            # Remove all deferred statements referencing the temporary table.
-            for sql in list(self.deferred_sql):
-                if isinstance(sql, Statement) and sql.references_table(temp_model._meta.db_table):
-                    self.deferred_sql.remove(sql)
-
             # Create a new table with the updated schema.
             self.create_model(temp_model)
 
@@ -226,6 +221,10 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             self.execute(self.sql_delete_table % {
                 "table": self.quote_name(model._meta.db_table),
             })
+            # Remove all deferred statements referencing the deleted table.
+            for sql in list(self.deferred_sql):
+                if isinstance(sql, Statement) and sql.references_table(model._meta.db_table):
+                    self.deferred_sql.remove(sql)
 
     def add_field(self, model, field):
         """
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index f4612a5dee..b889f6cda1 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -195,14 +195,15 @@ class SchemaTests(TransactionTestCase):
         """
         Tries creating a model's table, and then deleting it.
         """
-        # Create the table
         with connection.schema_editor() as editor:
+            # Create the table
             editor.create_model(Author)
-        # The table is there
-        list(Author.objects.all())
-        # Clean up that table
-        with connection.schema_editor() as editor:
+            # The table is there
+            list(Author.objects.all())
+            # Clean up that table
             editor.delete_model(Author)
+            # No deferred SQL should be left over.
+            self.assertEqual(editor.deferred_sql, [])
         # The table is gone
         with self.assertRaises(DatabaseError):
             list(Author.objects.all())
@@ -379,6 +380,17 @@ class SchemaTests(TransactionTestCase):
         self.assertEqual(columns['age'][0], "IntegerField")
         self.assertEqual(columns['age'][1][6], True)
 
+    def test_add_field_remove_field(self):
+        """
+        Adding a field and removing it removes all deferred sql referring to it.
+        """
+        with connection.schema_editor() as editor:
+            # Create a table with a unique constraint on the slug field.
+            editor.create_model(Tag)
+            # Remove the slug column.
+            editor.remove_field(Tag, Tag._meta.get_field('slug'))
+        self.assertEqual(editor.deferred_sql, [])
+
     def test_add_field_temp_default(self):
         """
         Tests adding fields to models with a temporary default