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Code Issues 32 Releases Wiki Activity

Removed reduce() usage in makemigrations; refs #23796.

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A lambda all_items_equal() replaced a reduce() that was broken for potential
3+-way merges. A reduce(operator.eq, ...) accumulates bools and can't
generically check equality of all items in a sequence:

>>> bool(reduce(operator.eq, [('migrations', '0001_initial')] * 3))
False

The code now counts the number of common ancestors to calculate slice offsets
for the branches. Each branch shares the same number of common ancestors.

The common_ancestor for loop statement had incomplete branch coverage.
This commit is contained in:
Brad Walker
2014-11-12 16:06:12 -07:00
committed by Tim Graham
parent cfa26f29bd
commit 54d3dcbc51
1 changed files with 11 additions and 17 deletions
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28
django/core/management/commands/makemigrations.py
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@@ -1,6 +1,6 @@
from itertools import takewhile
import sys
import os
import operator
from django.apps import apps
from django.core.management.base import BaseCommand, CommandError
@@ -11,7 +11,7 @@ from django.db.migrations.questioner import MigrationQuestioner, InteractiveMigr
from django.db.migrations.state import ProjectState
from django.db.migrations.writer import MigrationWriter
from django.utils.six import iteritems
from django.utils.six.moves import reduce
from django.utils.six.moves import zip
class Command(BaseCommand):
@@ -187,24 +187,18 @@ class Command(BaseCommand):
migration = loader.get_migration(app_label, migration_name)
migration.ancestry = loader.graph.forwards_plan((app_label, migration_name))
merge_migrations.append(migration)
common_ancestor = None
for level in zip(*[m.ancestry for m in merge_migrations]):
if reduce(operator.eq, level):
common_ancestor = level[0]
else:
break
if common_ancestor is None:
all_items_equal = lambda seq: all(item == seq[0] for item in seq[1:])
merge_migrations_generations = zip(*[m.ancestry for m in merge_migrations])
common_ancestor_count = sum(1 for common_ancestor_generation
in takewhile(all_items_equal, merge_migrations_generations))
if not common_ancestor_count:
raise ValueError("Could not find common ancestor of %s" % migration_names)
# Now work out the operations along each divergent branch
for migration in merge_migrations:
migration.branch = migration.ancestry[
(migration.ancestry.index(common_ancestor) + 1):
]
migration.merged_operations = []
for node_app, node_name in migration.branch:
migration.merged_operations.extend(
loader.get_migration(node_app, node_name).operations
)
migration.branch = migration.ancestry[common_ancestor_count:]
migrations_ops = (loader.get_migration(node_app, node_name).operations
for node_app, node_name in migration.branch)
migration.merged_operations = sum(migrations_ops, [])
# In future, this could use some of the Optimizer code
# (can_optimize_through) to automatically see if they're
# mergeable. For now, we always just prompt the user.