From d7ab2cefb7ec94bf45d37a02c79b6703ea2880e5 Mon Sep 17 00:00:00 2001
From: Tim Graham <timograham@gmail.com>
Date: Wed, 24 Sep 2014 15:49:30 -0400
Subject: [PATCH] Revert "Fixed #23474 -- Prevented migrating backwards from
 unapplying the wrong migrations."

This reverts commit abcf28a07695a45cb5fb15b81bffc97bea5e0be3.
---
 django/db/migrations/executor.py              | 14 +++----
 docs/releases/1.7.1.txt                       |  3 --
 tests/migrations/test_executor.py             | 38 -------------------
 .../__init__.py                               |  0
 .../0001_initial.py                           | 16 --------
 .../__init__.py                               |  0
 6 files changed, 5 insertions(+), 66 deletions(-)
 delete mode 100644 tests/migrations/test_migrations_backwards_deps_1/__init__.py
 delete mode 100644 tests/migrations2/test_migrations_backwards_deps_2/0001_initial.py
 delete mode 100644 tests/migrations2/test_migrations_backwards_deps_2/__init__.py

diff --git a/django/db/migrations/executor.py b/django/db/migrations/executor.py
index 6ebb21fc0ba..32aa82b82c7 100644
--- a/django/db/migrations/executor.py
+++ b/django/db/migrations/executor.py
@@ -36,15 +36,11 @@ class MigrationExecutor(object):
             # If the migration is already applied, do backwards mode,
             # otherwise do forwards mode.
             elif target in applied:
-                app_label = target[0]
-                next_migration_prefix = str(int(target[1][:4]) + 1)
-                try:
-                    next_migration = self.loader.get_migration_by_prefix(app_label, next_migration_prefix)
-                except KeyError:
-                    # If `target` is the most recent one in its app, there is nothing to do.
-                    pass
-                else:
-                    backwards_plan = self.loader.graph.backwards_plan(next_migration)
+                backwards_plan = self.loader.graph.backwards_plan(target)[:-1]
+                # We only do this if the migration is not the most recent one
+                # in its app - that is, another migration with the same app
+                # label is in the backwards plan
+                if any(node[0] == target[0] for node in backwards_plan):
                     for migration in backwards_plan:
                         if migration in applied:
                             plan.append((self.loader.graph.nodes[migration], True))
diff --git a/docs/releases/1.7.1.txt b/docs/releases/1.7.1.txt
index ceed11087bf..cd534f13466 100644
--- a/docs/releases/1.7.1.txt
+++ b/docs/releases/1.7.1.txt
@@ -47,9 +47,6 @@ Bugfixes
 * Allowed migrations to work with ``app_label``\s that have the same last
   part (e.g. ``django.contrib.auth`` and ``vendor.auth``) (:ticket:`23483`).
 
-* Fixed bug in migrations that could cause unexpected data loss when executing
-  a backwards or no-op migration (:ticket:`23474`).
-
 * Restored the ability to deepcopy ``F`` objects (:ticket:`23492`).
 
 * Formats for Welsh (``cy``) and several Chinese locales (``zh_CN``,
diff --git a/tests/migrations/test_executor.py b/tests/migrations/test_executor.py
index 222f1b847e0..b8eddc6f972 100644
--- a/tests/migrations/test_executor.py
+++ b/tests/migrations/test_executor.py
@@ -231,41 +231,3 @@ class ExecutorTests(MigrationTestBase):
         executor.migrate([("migrations", None)])
         self.assertTableNotExists("migrations_author")
         self.assertTableNotExists("migrations_tribble")
-
-    @override_settings(
-        MIGRATION_MODULES={
-            "migrations": "migrations.test_migrations_backwards_deps_1",
-            "migrations2": "migrations2.test_migrations_backwards_deps_2",
-        },
-    )
-    def test_backwards_deps(self):
-        """
-        #23474 - Migrating backwards shouldn't cause the wrong migrations to be
-        unapplied.
-
-        Migration dependencies (x -> y === y depends on x):
-        m.0001 -+-> m.0002
-                +-> m2.0001
-
-        1) Migrate m2 to 0001, causing { m.0001, m2.0002 } to be applied.
-        2) Migrate m to 0001. m.0001 has already been applied, so this should
-           be a noop.
-        """
-        executor = MigrationExecutor(connection)
-        executor.migrate([("migrations2", "0001_initial")])
-        try:
-            self.assertTableExists("migrations2_example")
-            # Rebuild the graph to reflect the new DB state
-            executor.loader.build_graph()
-            self.assertEqual(
-                executor.migration_plan([("migrations", "0001_initial")]),
-                [],
-            )
-            executor.migrate([("migrations", "0001_initial")])
-            self.assertTableExists("migrations2_example")
-        finally:
-            # And migrate back to clean up the database
-            executor.loader.build_graph()
-            executor.migrate([("migrations", None)])
-            self.assertTableNotExists("migrations_author")
-            self.assertTableNotExists("migrations_tribble")
diff --git a/tests/migrations/test_migrations_backwards_deps_1/__init__.py b/tests/migrations/test_migrations_backwards_deps_1/__init__.py
deleted file mode 100644
index e69de29bb2d..00000000000
diff --git a/tests/migrations2/test_migrations_backwards_deps_2/0001_initial.py b/tests/migrations2/test_migrations_backwards_deps_2/0001_initial.py
deleted file mode 100644
index 0b6eafb02f9..00000000000
--- a/tests/migrations2/test_migrations_backwards_deps_2/0001_initial.py
+++ /dev/null
@@ -1,16 +0,0 @@
-# -*- coding: utf-8 -*-
-from __future__ import unicode_literals
-
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-    dependencies = [('migrations', '0001_initial')]
-    operations = [
-        migrations.CreateModel(
-            "Example",
-            [
-                ("id", models.AutoField(primary_key=True)),
-            ],
-        ),
-    ]
diff --git a/tests/migrations2/test_migrations_backwards_deps_2/__init__.py b/tests/migrations2/test_migrations_backwards_deps_2/__init__.py
deleted file mode 100644
index e69de29bb2d..00000000000