Fixed #24110 -- Rewrote migration unapply to preserve intermediate states (fdc2cc94) · Commits · Dom Sekotill / django

django/db/migrations/migration.py

+26 −15

Original line number	Diff line number	Diff line
		@@ -115,28 +115,39 @@ class Migration(object):
		Takes a project_state representing all migrations prior to this one
		and a schema_editor for a live database and applies the migration
		in a reverse order.

		The backwards migration process consists of two phases:

		1. The intermediate states from right before the first until right
		after the last opertion inside this migration are preserved.
		2. The operations are applied in reverse order using the states
		recorded in step 1.
		"""
		# We need to pre-calculate the stack of project states
		# Construct all the intermediate states we need for a reverse migration
		to_run = []
		new_state = project_state
		# Phase 1
		for operation in self.operations:
		# If this operation cannot be represented as SQL, place a comment
		# there instead
		if collect_sql and not operation.reduces_to_sql:
		# If it's irreversible, error out
		if not operation.reversible:
		raise Migration.IrreversibleError("Operation %s in %s is not reversible" % (operation, self))
		# Preserve new state from previous run to not tamper the same state
		# over all operations
		new_state = new_state.clone()
		old_state = new_state.clone()
		operation.state_forwards(self.app_label, new_state)
		to_run.insert(0, (operation, old_state, new_state))

		# Phase 2
		for operation, to_state, from_state in to_run:
		if collect_sql:
		if not operation.reduces_to_sql:
		schema_editor.collected_sql.append("--")
		schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE "
		"WRITTEN AS SQL:")
		schema_editor.collected_sql.append("-- %s" % operation.describe())
		schema_editor.collected_sql.append("--")
		continue
		# If it's irreversible, error out
		if not operation.reversible:
		raise Migration.IrreversibleError("Operation %s in %s is not reversible" % (operation, self))
		old_state = project_state.clone()
		operation.state_forwards(self.app_label, project_state)
		to_run.append((operation, old_state, project_state))
		# Now run them in reverse
		to_run.reverse()
		for operation, to_state, from_state in to_run:
		if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
		# We're forcing a transaction on a non-transactional-DDL backend
		with atomic(schema_editor.connection.alias):

docs/releases/1.7.3.txt

+2 −0

Original line number	Diff line number	Diff line
		@@ -26,3 +26,5 @@ Bugfixes
		(:ticket:`24097`).

		* Added correct formats for Greek (``el``) (:ticket:`23967`).

		* Fixed a migration crash when unapplying a migration (:ticket:`24110`).

tests/migrations/test_operations.py

+17 −11

Original line number	Diff line number	Diff line
		@@ -465,27 +465,33 @@ class OperationTests(OperationTestBase):
		# Test the state alteration
		operation = migrations.RenameModel("Pony", "Horse")
		self.assertEqual(operation.describe(), "Rename model Pony to Horse")
		new_state = project_state.clone()
		operation.state_forwards("test_rnmo", new_state)
		self.assertNotIn(("test_rnmo", "pony"), new_state.models)
		self.assertIn(("test_rnmo", "horse"), new_state.models)
		# Remember, RenameModel also repoints all incoming FKs and M2Ms
		self.assertEqual("test_rnmo.Horse", new_state.models["test_rnmo", "rider"].fields[1][1].rel.to)
		# Test the database alteration
		# Test initial state and database
		self.assertIn(("test_rnmo", "pony"), project_state.models)
		self.assertNotIn(("test_rnmo", "horse"), project_state.models)
		self.assertTableExists("test_rnmo_pony")
		self.assertTableNotExists("test_rnmo_horse")
		if connection.features.supports_foreign_keys:
		self.assertFKExists("test_rnmo_rider", ["pony_id"], ("test_rnmo_pony", "id"))
		self.assertFKNotExists("test_rnmo_rider", ["pony_id"], ("test_rnmo_horse", "id"))
		with connection.schema_editor() as editor:
		operation.database_forwards("test_rnmo", editor, project_state, new_state)
		# Migrate forwards
		new_state = project_state.clone()
		new_state = self.apply_operations("test_rnmo", new_state, [operation])
		# Test new state and database
		self.assertNotIn(("test_rnmo", "pony"), new_state.models)
		self.assertIn(("test_rnmo", "horse"), new_state.models)
		# RenameModel also repoints all incoming FKs and M2Ms
		self.assertEqual("test_rnmo.Horse", new_state.models["test_rnmo", "rider"].fields[1][1].rel.to)
		self.assertTableNotExists("test_rnmo_pony")
		self.assertTableExists("test_rnmo_horse")
		if connection.features.supports_foreign_keys:
		self.assertFKNotExists("test_rnmo_rider", ["pony_id"], ("test_rnmo_pony", "id"))
		self.assertFKExists("test_rnmo_rider", ["pony_id"], ("test_rnmo_horse", "id"))
		# And test reversal
		self.unapply_operations("test_rnmo", project_state, [operation])
		# Migrate backwards
		original_state = self.unapply_operations("test_rnmo", project_state, [operation])
		# Test original state and database
		self.assertIn(("test_rnmo", "pony"), original_state.models)
		self.assertNotIn(("test_rnmo", "horse"), original_state.models)
		self.assertEqual("Pony", original_state.models["test_rnmo", "rider"].fields[1][1].rel.to)
		self.assertTableExists("test_rnmo_pony")
		self.assertTableNotExists("test_rnmo_horse")
		if connection.features.supports_foreign_keys: