Fixed #24900 -- Allowed migrating backward to squashed migrations.

2 files changed, 37 insertions, 0 deletions

diff --git a/tests/migrations/test_commands.py b/tests/migrations/test_commands.py
index 563b1bd146..d545f125dd 100644
--- a/tests/migrations/test_commands.py
+++ b/tests/migrations/test_commands.py
@@ -980,6 +980,19 @@ class MigrateTests(MigrationTestBase):
                 # Unmigrate everything.
                 call_command('migrate', 'migrations', 'zero', verbosity=0)
 
+    @override_settings(MIGRATION_MODULES={'migrations': 'migrations.test_migrations_squashed'})
+    def test_migrate_backward_to_squashed_migration(self):
+        try:
+            call_command('migrate', 'migrations', '0001_squashed_0002', verbosity=0)
+            self.assertTableExists('migrations_author')
+            self.assertTableExists('migrations_book')
+            call_command('migrate', 'migrations', '0001_initial', verbosity=0)
+            self.assertTableExists('migrations_author')
+            self.assertTableNotExists('migrations_book')
+        finally:
+            # Unmigrate everything.
+            call_command('migrate', 'migrations', 'zero', verbosity=0)
+
     @override_settings(MIGRATION_MODULES={'migrations': 'migrations.test_migrations'})
     def test_migrate_inconsistent_history(self):
         """
diff --git a/tests/migrations/test_executor.py b/tests/migrations/test_executor.py
index fc80c950fa..f8c321b0f3 100644
--- a/tests/migrations/test_executor.py
+++ b/tests/migrations/test_executor.py
@@ -104,6 +104,29 @@ class ExecutorTests(MigrationTestBase):
         self.assertTableNotExists("migrations_author")
         self.assertTableNotExists("migrations_book")
 
+    @override_settings(
+        MIGRATION_MODULES={'migrations': 'migrations.test_migrations_squashed'},
+    )
+    def test_migrate_backward_to_squashed_migration(self):
+        executor = MigrationExecutor(connection)
+        try:
+            self.assertTableNotExists('migrations_author')
+            self.assertTableNotExists('migrations_book')
+            executor.migrate([('migrations', '0001_squashed_0002')])
+            self.assertTableExists('migrations_author')
+            self.assertTableExists('migrations_book')
+            executor.loader.build_graph()
+            # Migrate backward to a squashed migration.
+            executor.migrate([('migrations', '0001_initial')])
+            self.assertTableExists('migrations_author')
+            self.assertTableNotExists('migrations_book')
+        finally:
+            # Unmigrate everything.
+            executor = MigrationExecutor(connection)
+            executor.migrate([('migrations', None)])
+            self.assertTableNotExists('migrations_author')
+            self.assertTableNotExists('migrations_book')
+
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_non_atomic"})
     def test_non_atomic_migration(self):
         """
@@ -733,6 +756,7 @@ class FakeLoader:
     def __init__(self, graph, applied):
         self.graph = graph
         self.applied_migrations = applied
+        self.replace_migrations = True
 
 
 class FakeMigration: