Commit 6d2cad14 authored by Andrew Godwin's avatar Andrew Godwin
Browse files

Merge pull request #3525 from vanschelven/master 

Use topological sort for migration operation dependency resolution
parents 4f90c996 13d613f8

AUTHORS

+1 −0
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@@ -377,6 +377,7 @@ answer newbie questions, and generally made Django that much better: 
    Kevin McConnell <kevin.mcconnell@gmail.com>

    Kieran Holland <http://www.kieranholland.com>

    kilian <kilian.cavalotti@lip6.fr>

    Klaas van Schelven <klaas@vanschelven.com>

    knox <christobzr@gmail.com>

    konrad@gwu.edu

    Kowito Charoenratchatabhan <kowito@felspar.com>

django/db/migrations/autodetector.py

+15 −22
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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.operations.models import AlterModelOptions



from .topological_sort import stable_topological_sort





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

        # inside the same app

        for app_label, ops in sorted(self.generated_operations.items()):

            for i in range(10000):

                found = False

                for i, op in enumerate(ops):



            # construct a dependency-graph for in-app dependencies

            dependency_graph = dict((op, set()) for op in ops)

            for op in ops:

                for dep in op._auto_deps:

                    if dep[0] == app_label:

                            # Alright, there's a dependency on the same app.

                            for j, op2 in enumerate(ops):

                                if j > i and self.check_dependency(op2, dep):

                                    # shift the operation from position i after

                                    # the operation at position j

                                    ops = ops[:i] + ops[i + 1:j + 1] + [op] + ops[j + 1:]

                                    found = True

                                    break

                        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

                        for op2 in ops:

                            if self.check_dependency(op2, dep):

                                dependency_graph[op].add(op2)



            # we use a stable sort for deterministic tests & general behavior

            self.generated_operations[app_label] = stable_topological_sort(

                ops, dependency_graph)



        # Now, we need to chop the lists of operations up into migrations with

        # dependencies on each other.

django/db/migrations/topological_sort.py

0 → 100644
+34 −0
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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

tests/migrations/test_autodetector.py

+3 −3
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@@ -1107,12 +1107,12 @@ class AutodetectorTests(TestCase): 
        # Right number of migrations?

        self.assertNumberMigrations(changes, "testapp", 1)

        # 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?

        self.assertOperationAttributes(changes, "testapp", 0, 0, name="publishers")

        self.assertOperationAttributes(changes, "testapp", 0, 1, name="author")

        self.assertOperationAttributes(changes, "testapp", 0, 2, name="Author")

        self.assertOperationAttributes(changes, "testapp", 0, 3, name="publisher")

        self.assertOperationAttributes(changes, "testapp", 0, 2, name="publisher")

        self.assertOperationAttributes(changes, "testapp", 0, 3, name="Author")

        self.assertOperationAttributes(changes, "testapp", 0, 4, name="Contract")



    def test_non_circular_foreignkey_dependency_removal(self):