Add root_node and leaf_node functions to MigrationGraph (8a1f0177) · Commits · Dom Sekotill / django

django/db/migrations/graph.py

+28 −2

Original line number	Diff line number	Diff line
		@@ -19,8 +19,9 @@ class MigrationGraph(object):
		replacing migration, and repoint any dependencies that pointed to the
		replaced migrations to point to the replacing one.

		A node should be a tuple: (app_path, migration_name) - but the code
		here doesn't really care.
		A node should be a tuple: (app_path, migration_name). The tree special-cases
		things within an app - namely, root nodes and leaf nodes ignore dependencies
		to other apps.
		"""

		def __init__(self):
		@@ -59,6 +60,31 @@ class MigrationGraph(object):
		raise ValueError("Node %r not a valid node" % node)
		return self.dfs(node, lambda x: self.dependents.get(x, set()))

		def root_nodes(self):
		"""
		Returns all root nodes - that is, nodes with no dependencies inside
		their app. These are the starting point for an app.
		"""
		roots = set()
		for node in self.nodes:
		if not filter(lambda key: key[0] == node[0], self.dependencies.get(node, set())):
		roots.add(node)
		return roots

		def leaf_nodes(self):
		"""
		Returns all leaf nodes - that is, nodes with no dependents in their app.
		These are the "most current" version of an app's schema.
		Having more than one per app is technically an error, but one that
		gets handled further up, in the interactive command - it's usually the
		result of a VCS merge and needs some user input.
		"""
		leaves = set()
		for node in self.nodes:
		if not filter(lambda key: key[0] == node[0], self.dependents.get(node, set())):
		leaves.add(node)
		return leaves

		def dfs(self, start, get_children):
		"""
		Dynamic programming based depth first search, for finding dependencies.

tests/migrations/tests.py

+18 −0

Original line number	Diff line number	Diff line
		@@ -44,6 +44,15 @@ class GraphTests(TransactionTestCase):
		graph.backwards_plan(("app_b", "0002")),
		[('app_a', '0004'), ('app_a', '0003'), ('app_b', '0002')],
		)
		# Test roots and leaves
		self.assertEqual(
		graph.root_nodes(),
		set([('app_a', '0001'), ('app_b', '0001')]),
		)
		self.assertEqual(
		graph.leaf_nodes(),
		set([('app_a', '0004'), ('app_b', '0002')]),
		)

		def test_complex_graph(self):
		"""
		@@ -81,6 +90,15 @@ class GraphTests(TransactionTestCase):
		graph.backwards_plan(("app_b", "0001")),
		[('app_a', '0004'), ('app_c', '0002'), ('app_c', '0001'), ('app_a', '0003'), ('app_b', '0002'), ('app_b', '0001')],
		)
		# Test roots and leaves
		self.assertEqual(
		graph.root_nodes(),
		set([('app_a', '0001'), ('app_b', '0001'), ('app_c', '0001')]),
		)
		self.assertEqual(
		graph.leaf_nodes(),
		set([('app_a', '0004'), ('app_b', '0002'), ('app_c', '0002')]),
		)

		def test_circular_graph(self):
		"""