Fix migration planner to fully understand squashed migrations. And test.

django/db/migrations/executor.py

@@ -11,7 +11,6 @@ class MigrationExecutor(object):
     def __init__(self, connection, progress_callback=None):
         self.connection = connection
         self.loader = MigrationLoader(self.connection)
-        self.loader.load_disk()
         self.recorder = MigrationRecorder(self.connection)
         self.progress_callback = progress_callback
 
@@ -20,7 +19,7 @@ def migration_plan(self, targets):
         Given a set of targets, returns a list of (Migration instance, backwards?).
         """
         plan = []
-        applied = self.recorder.applied_migrations()
+        applied = set(self.loader.applied_migrations)
         for target in targets:
             # If the target is (appname, None), that means unmigrate everything
             if target[1] is None:
@@ -87,7 +86,13 @@ def apply_migration(self, migration, fake=False):
             with self.connection.schema_editor() as schema_editor:
                 project_state = self.loader.graph.project_state((migration.app_label, migration.name), at_end=False)
                 migration.apply(project_state, schema_editor)
-        self.recorder.record_applied(migration.app_label, migration.name)
+        # For replacement migrations, record individual statuses
+        if migration.replaces:
+            for app_label, name in migration.replaces:
+                self.recorder.record_applied(app_label, name)
+        else:
+            self.recorder.record_applied(migration.app_label, migration.name)
+        # Report prgress
         if self.progress_callback:
             self.progress_callback("apply_success", migration)
 
@@ -101,6 +106,12 @@ def unapply_migration(self, migration, fake=False):
             with self.connection.schema_editor() as schema_editor:
                 project_state = self.loader.graph.project_state((migration.app_label, migration.name), at_end=False)
                 migration.unapply(project_state, schema_editor)
-        self.recorder.record_unapplied(migration.app_label, migration.name)
+        # For replacement migrations, record individual statuses
+        if migration.replaces:
+            for app_label, name in migration.replaces:
+                self.recorder.record_unapplied(app_label, name)
+        else:
+            self.recorder.record_unapplied(migration.app_label, migration.name)
+        # Report progress
         if self.progress_callback:
             self.progress_callback("unapply_success", migration)

django/db/migrations/loader.py

@@ -1,9 +1,10 @@
 import os
+import sys
 from importlib import import_module
-from django.utils.functional import cached_property
 from django.db.models.loading import cache
 from django.db.migrations.recorder import MigrationRecorder
 from django.db.migrations.graph import MigrationGraph
+from django.utils import six
 from django.conf import settings
 
 
@@ -32,10 +33,12 @@ class MigrationLoader(object):
     in memory.
     """
 
-    def __init__(self, connection):
+    def __init__(self, connection, load=True):
         self.connection = connection
         self.disk_migrations = None
         self.applied_migrations = None
+        if load:
+            self.build_graph()
 
     @classmethod
     def migrations_module(cls, app_label):
@@ -55,6 +58,7 @@ def load_disk(self):
             # Get the migrations module directory
             app_label = app.__name__.split(".")[-2]
             module_name = self.migrations_module(app_label)
+            was_loaded = module_name in sys.modules
             try:
                 module = import_module(module_name)
             except ImportError as e:
@@ -71,6 +75,9 @@ def load_disk(self):
                 # Module is not a package (e.g. migrations.py).
                 if not hasattr(module, '__path__'):
                     continue
+                # Force a reload if it's already loaded (tests need this)
+                if was_loaded:
+                    six.moves.reload_module(module)
             self.migrated_apps.add(app_label)
             directory = os.path.dirname(module.__file__)
             # Scan for .py[c|o] files
@@ -107,9 +114,6 @@ def get_migration(self, app_label, name_prefix):
 
     def get_migration_by_prefix(self, app_label, name_prefix):
         "Returns the migration(s) which match the given app label and name _prefix_"
-        # Make sure we have the disk data
-        if self.disk_migrations is None:
-            self.load_disk()
         # Do the search
         results = []
         for l, n in self.disk_migrations:
@@ -122,18 +126,17 @@ def get_migration_by_prefix(self, app_label, name_prefix):
         else:
             return self.disk_migrations[results[0]]
 
-    @cached_property
-    def graph(self):
+    def build_graph(self):
         """
         Builds a migration dependency graph using both the disk and database.
+        You'll need to rebuild the graph if you apply migrations. This isn't
+        usually a problem as generally migration stuff runs in a one-shot process.
         """
-        # Make sure we have the disk data
-        if self.disk_migrations is None:
-            self.load_disk()
-        # And the database data
-        if self.applied_migrations is None:
-            recorder = MigrationRecorder(self.connection)
-            self.applied_migrations = recorder.applied_migrations()
+        # Load disk data
+        self.load_disk()
+        # Load database data
+        recorder = MigrationRecorder(self.connection)
+        self.applied_migrations = recorder.applied_migrations()
         # Do a first pass to separate out replacing and non-replacing migrations
         normal = {}
         replacing = {}
@@ -152,12 +155,12 @@ def graph(self):
         # Carry out replacements if we can - that is, if all replaced migrations
         # are either unapplied or missing.
         for key, migration in replacing.items():
-            # Do the check
-            can_replace = True
-            for target in migration.replaces:
-                if target in self.applied_migrations:
-                    can_replace = False
-                    break
+            # Ensure this replacement migration is not in applied_migrations
+            self.applied_migrations.discard(key)
+            # Do the check. We can replace if all our replace targets are
+            # applied, or if all of them are unapplied.
+            applied_statuses = [(target in self.applied_migrations) for target in migration.replaces]
+            can_replace = all(applied_statuses) or (not any(applied_statuses))
             if not can_replace:
                 continue
             # Alright, time to replace. Step through the replaced migrations
@@ -171,14 +174,16 @@ def graph(self):
                     normal[child_key].dependencies.remove(replaced)
                     normal[child_key].dependencies.append(key)
             normal[key] = migration
+            # Mark the replacement as applied if all its replaced ones are
+            if all(applied_statuses):
+                self.applied_migrations.add(key)
         # Finally, make a graph and load everything into it
-        graph = MigrationGraph()
+        self.graph = MigrationGraph()
         for key, migration in normal.items():
-            graph.add_node(key, migration)
+            self.graph.add_node(key, migration)
         for key, migration in normal.items():
             for parent in migration.dependencies:
-                graph.add_dependency(key, parent)
-        return graph
+                self.graph.add_dependency(key, parent)
 
 
 class BadMigrationError(Exception):

django/db/migrations/migration.py

@@ -39,6 +39,11 @@ class IrreversibleError(RuntimeError):
     def __init__(self, name, app_label):
         self.name = name
         self.app_label = app_label
+        # Copy dependencies & other attrs as we might mutate them at runtime
+        self.operations = list(self.__class__.operations)
+        self.dependencies = list(self.__class__.dependencies)
+        self.run_before = list(self.__class__.run_before)
+        self.replaces = list(self.__class__.replaces)
 
     def __eq__(self, other):
         if not isinstance(other, Migration):

tests/migrations/test_executor.py

@@ -38,7 +38,58 @@ def test_run(self):
         # Are the tables there now?
         self.assertIn("migrations_author", connection.introspection.get_table_list(connection.cursor()))
         self.assertIn("migrations_book", connection.introspection.get_table_list(connection.cursor()))
+        # Rebuild the graph to reflect the new DB state
+        executor.loader.build_graph()
         # Alright, let's undo what we did
+        plan = executor.migration_plan([("migrations", None)])
+        self.assertEqual(
+            plan,
+            [
+                (executor.loader.graph.nodes["migrations", "0002_second"], True),
+                (executor.loader.graph.nodes["migrations", "0001_initial"], True),
+            ],
+        )
+        executor.migrate([("migrations", None)])
+        # Are the tables gone?
+        self.assertNotIn("migrations_author", connection.introspection.get_table_list(connection.cursor()))
+        self.assertNotIn("migrations_book", connection.introspection.get_table_list(connection.cursor()))
+
+    @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_squashed"})
+    def test_run_with_squashed(self):
+        """
+        Tests running a squashed migration from zero (should ignore what it replaces)
+        """
+        executor = MigrationExecutor(connection)
+        executor.recorder.flush()
+        # Check our leaf node is the squashed one
+        leaves = [key for key in executor.loader.graph.leaf_nodes() if key[0] == "migrations"]
+        self.assertEqual(leaves, [("migrations", "0001_squashed_0002")])
+        # Check the plan
+        plan = executor.migration_plan([("migrations", "0001_squashed_0002")])
+        self.assertEqual(
+            plan,
+            [
+                (executor.loader.graph.nodes["migrations", "0001_squashed_0002"], False),
+            ],
+        )
+        # Were the tables there before?
+        self.assertNotIn("migrations_author", connection.introspection.get_table_list(connection.cursor()))
+        self.assertNotIn("migrations_book", connection.introspection.get_table_list(connection.cursor()))
+        # Alright, let's try running it
+        executor.migrate([("migrations", "0001_squashed_0002")])
+        # Are the tables there now?
+        self.assertIn("migrations_author", connection.introspection.get_table_list(connection.cursor()))
+        self.assertIn("migrations_book", connection.introspection.get_table_list(connection.cursor()))
+        # Rebuild the graph to reflect the new DB state
+        executor.loader.build_graph()
+        # Alright, let's undo what we did. Should also just use squashed.
+        plan = executor.migration_plan([("migrations", None)])
+        self.assertEqual(
+            plan,
+            [
+                (executor.loader.graph.nodes["migrations", "0001_squashed_0002"], True),
+            ],
+        )
         executor.migrate([("migrations", None)])
         # Are the tables gone?
         self.assertNotIn("migrations_author", connection.introspection.get_table_list(connection.cursor()))
@@ -70,6 +121,8 @@ def test_empty_plan(self):
         )
         # Fake-apply all migrations
         executor.migrate([("migrations", "0002_second"), ("sessions", "0001_initial")], fake=True)
+        # Rebuild the graph to reflect the new DB state
+        executor.loader.build_graph()
         # Now plan a second time and make sure it's empty
         plan = executor.migration_plan([("migrations", "0002_second"), ("sessions", "0001_initial")])
         self.assertEqual(plan, [])

tests/migrations/test_loader.py

@@ -82,21 +82,34 @@ def test_name_match(self):
             migration_loader.get_migration_by_prefix("migrations", "blarg")
 
     def test_load_import_error(self):
-        migration_loader = MigrationLoader(connection)
-
         with override_settings(MIGRATION_MODULES={"migrations": "migrations.faulty_migrations.import_error"}):
             with self.assertRaises(ImportError):
-                migration_loader.load_disk()
+                MigrationLoader(connection)
 
     def test_load_module_file(self):
-        migration_loader = MigrationLoader(connection)
-
         with override_settings(MIGRATION_MODULES={"migrations": "migrations.faulty_migrations.file"}):
-            migration_loader.load_disk()
+            MigrationLoader(connection)
 
     @skipIf(six.PY2, "PY2 doesn't load empty dirs.")
     def test_load_empty_dir(self):
-        migration_loader = MigrationLoader(connection)
-
         with override_settings(MIGRATION_MODULES={"migrations": "migrations.faulty_migrations.namespace"}):
-            migration_loader.load_disk()
+            MigrationLoader(connection)
+
+    @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_squashed"})
+    def test_loading_squashed(self):
+        "Tests loading a squashed migration"
+        migration_loader = MigrationLoader(connection)
+        recorder = MigrationRecorder(connection)
+        # Loading with nothing applied should just give us the one node
+        self.assertEqual(
+            len(migration_loader.graph.nodes),
+            1,
+        )
+        # However, fake-apply one migration and it should now use the old two
+        recorder.record_applied("migrations", "0001_initial")
+        migration_loader.build_graph()
+        self.assertEqual(
+            len(migration_loader.graph.nodes),
+            2,
+        )
+        recorder.flush()

tests/migrations/test_migrations_squashed/0001_initial.py

@@ -0,0 +1,27 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    operations = [
+
+        migrations.CreateModel(
+            "Author",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("silly_field", models.BooleanField(default=False)),
+            ],
+        ),
+
+        migrations.CreateModel(
+            "Tribble",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("fluffy", models.BooleanField(default=True)),
+            ],
+        )
+
+    ]

tests/migrations/test_migrations_squashed/0001_squashed_0002.py

@@ -0,0 +1,32 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    replaces = [
+        ("migrations", "0001_initial"),
+        ("migrations", "0002_second"),
+    ]
+
+    operations = [
+
+        migrations.CreateModel(
+            "Author",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("rating", models.IntegerField(default=0)),
+            ],
+        ),
+
+        migrations.CreateModel(
+            "Book",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("author", models.ForeignKey("migrations.Author", null=True)),
+            ],
+        ),
+
+    ]

tests/migrations/test_migrations_squashed/0002_second.py

@@ -0,0 +1,24 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("migrations", "0001_initial")]
+
+    operations = [
+
+        migrations.DeleteModel("Tribble"),
+
+        migrations.RemoveField("Author", "silly_field"),
+
+        migrations.AddField("Author", "rating", models.IntegerField(default=0)),
+
+        migrations.CreateModel(
+            "Book",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("author", models.ForeignKey("migrations.Author", null=True)),
+            ],
+        )
+
+    ]