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Merge pull request #3525 from vanschelven/master

Use topological sort for migration operation dependency resolution
This commit is contained in:
Andrew Godwin 2014-11-15 14:53:12 +01:00
commit 6d2cad14f7
4 changed files with 53 additions and 25 deletions

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@ -377,6 +377,7 @@ answer newbie questions, and generally made Django that much better:
Kevin McConnell <kevin.mcconnell@gmail.com> Kevin McConnell <kevin.mcconnell@gmail.com>
Kieran Holland <http://www.kieranholland.com> Kieran Holland <http://www.kieranholland.com>
kilian <kilian.cavalotti@lip6.fr> kilian <kilian.cavalotti@lip6.fr>
Klaas van Schelven <klaas@vanschelven.com>
knox <christobzr@gmail.com> knox <christobzr@gmail.com>
konrad@gwu.edu konrad@gwu.edu
Kowito Charoenratchatabhan <kowito@felspar.com> Kowito Charoenratchatabhan <kowito@felspar.com>

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@ -14,6 +14,8 @@ from django.db.migrations.questioner import MigrationQuestioner
from django.db.migrations.optimizer import MigrationOptimizer from django.db.migrations.optimizer import MigrationOptimizer
from django.db.migrations.operations.models import AlterModelOptions from django.db.migrations.operations.models import AlterModelOptions
from .topological_sort import stable_topological_sort
class MigrationAutodetector(object): class MigrationAutodetector(object):
""" """
@ -191,28 +193,19 @@ class MigrationAutodetector(object):
# isn't bad, but we need to pull a few things around so FKs work nicely # isn't bad, but we need to pull a few things around so FKs work nicely
# inside the same app # inside the same app
for app_label, ops in sorted(self.generated_operations.items()): for app_label, ops in sorted(self.generated_operations.items()):
for i in range(10000):
found = False # construct a dependency-graph for in-app dependencies
for i, op in enumerate(ops): dependency_graph = dict((op, set()) for op in ops)
for dep in op._auto_deps: for op in ops:
if dep[0] == app_label: for dep in op._auto_deps:
# Alright, there's a dependency on the same app. if dep[0] == app_label:
for j, op2 in enumerate(ops): for op2 in ops:
if j > i and self.check_dependency(op2, dep): if self.check_dependency(op2, dep):
# shift the operation from position i after dependency_graph[op].add(op2)
# the operation at position j
ops = ops[:i] + ops[i + 1:j + 1] + [op] + ops[j + 1:] # we use a stable sort for deterministic tests & general behavior
found = True self.generated_operations[app_label] = stable_topological_sort(
break ops, dependency_graph)
if found:
break
if found:
break
if not found:
break
else:
raise ValueError("Infinite loop caught in operation dependency resolution")
self.generated_operations[app_label] = ops
# Now, we need to chop the lists of operations up into migrations with # Now, we need to chop the lists of operations up into migrations with
# dependencies on each other. # dependencies on each other.

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@ -0,0 +1,34 @@
def topological_sort_as_sets(dependency_graph):
"""Variation of Kahn's algorithm (1962) that returns sets.
Takes a dependency graph as a dictionary of node => dependencies.
Yields sets of items in topological order, where the first set contains
all nodes without dependencies, and each following set contains all
nodes that depend on the nodes in the previously yielded sets.
"""
todo = dependency_graph.copy()
while todo:
current = set(node for node, deps in todo.items() if len(deps) == 0)
if not current:
raise ValueError('Cyclic dependency in graph: {}'.format(
', '.join(repr(x) for x in todo.items())))
yield current
# remove current from todo's nodes & dependencies
todo = {node: (dependencies - current) for node, dependencies in
todo.items() if node not in current}
def stable_topological_sort(l, dependency_graph):
result = []
for layer in topological_sort_as_sets(dependency_graph):
for node in l:
if node in layer:
result.append(node)
return result

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@ -1107,12 +1107,12 @@ class AutodetectorTests(TestCase):
# Right number of migrations? # Right number of migrations?
self.assertNumberMigrations(changes, "testapp", 1) self.assertNumberMigrations(changes, "testapp", 1)
# Right actions in right order? # Right actions in right order?
self.assertOperationTypes(changes, "testapp", 0, ["RemoveField", "RemoveField", "DeleteModel", "RemoveField", "DeleteModel"]) self.assertOperationTypes(changes, "testapp", 0, ["RemoveField", "RemoveField", "RemoveField", "DeleteModel", "DeleteModel"])
# Actions touching the right stuff? # Actions touching the right stuff?
self.assertOperationAttributes(changes, "testapp", 0, 0, name="publishers") self.assertOperationAttributes(changes, "testapp", 0, 0, name="publishers")
self.assertOperationAttributes(changes, "testapp", 0, 1, name="author") self.assertOperationAttributes(changes, "testapp", 0, 1, name="author")
self.assertOperationAttributes(changes, "testapp", 0, 2, name="Author") self.assertOperationAttributes(changes, "testapp", 0, 2, name="publisher")
self.assertOperationAttributes(changes, "testapp", 0, 3, name="publisher") self.assertOperationAttributes(changes, "testapp", 0, 3, name="Author")
self.assertOperationAttributes(changes, "testapp", 0, 4, name="Contract") self.assertOperationAttributes(changes, "testapp", 0, 4, name="Contract")
def test_non_circular_foreignkey_dependency_removal(self): def test_non_circular_foreignkey_dependency_removal(self):