323 lines
15 KiB
Python
323 lines
15 KiB
Python
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import pkgutil
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import sys
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from importlib import import_module, reload
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from django.apps import apps
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from django.conf import settings
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from django.db.migrations.graph import MigrationGraph
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from django.db.migrations.recorder import MigrationRecorder
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from .exceptions import (
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AmbiguityError, BadMigrationError, InconsistentMigrationHistory,
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NodeNotFoundError,
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)
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MIGRATIONS_MODULE_NAME = 'migrations'
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class MigrationLoader:
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"""
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Load migration files from disk and their status from the database.
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Migration files are expected to live in the "migrations" directory of
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an app. Their names are entirely unimportant from a code perspective,
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but will probably follow the 1234_name.py convention.
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On initialization, this class will scan those directories, and open and
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read the Python files, looking for a class called Migration, which should
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inherit from django.db.migrations.Migration. See
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django.db.migrations.migration for what that looks like.
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Some migrations will be marked as "replacing" another set of migrations.
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These are loaded into a separate set of migrations away from the main ones.
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If all the migrations they replace are either unapplied or missing from
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disk, then they are injected into the main set, replacing the named migrations.
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Any dependency pointers to the replaced migrations are re-pointed to the
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new migration.
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This does mean that this class MUST also talk to the database as well as
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to disk, but this is probably fine. We're already not just operating
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in memory.
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"""
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def __init__(self, connection, load=True, ignore_no_migrations=False):
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self.connection = connection
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self.disk_migrations = None
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self.applied_migrations = None
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self.ignore_no_migrations = ignore_no_migrations
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if load:
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self.build_graph()
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@classmethod
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def migrations_module(cls, app_label):
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"""
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Return the path to the migrations module for the specified app_label
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and a boolean indicating if the module is specified in
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settings.MIGRATION_MODULE.
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"""
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if app_label in settings.MIGRATION_MODULES:
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return settings.MIGRATION_MODULES[app_label], True
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else:
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app_package_name = apps.get_app_config(app_label).name
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return '%s.%s' % (app_package_name, MIGRATIONS_MODULE_NAME), False
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def load_disk(self):
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"""Load the migrations from all INSTALLED_APPS from disk."""
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self.disk_migrations = {}
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self.unmigrated_apps = set()
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self.migrated_apps = set()
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for app_config in apps.get_app_configs():
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# Get the migrations module directory
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module_name, explicit = self.migrations_module(app_config.label)
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if module_name is None:
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self.unmigrated_apps.add(app_config.label)
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continue
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was_loaded = module_name in sys.modules
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try:
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module = import_module(module_name)
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except ImportError as e:
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# I hate doing this, but I don't want to squash other import errors.
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# Might be better to try a directory check directly.
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if ((explicit and self.ignore_no_migrations) or (
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not explicit and "No module named" in str(e) and MIGRATIONS_MODULE_NAME in str(e))):
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self.unmigrated_apps.add(app_config.label)
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continue
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raise
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else:
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# Empty directories are namespaces.
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# getattr() needed on PY36 and older (replace w/attribute access).
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if getattr(module, '__file__', None) is None:
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self.unmigrated_apps.add(app_config.label)
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continue
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# Module is not a package (e.g. migrations.py).
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if not hasattr(module, '__path__'):
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self.unmigrated_apps.add(app_config.label)
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continue
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# Force a reload if it's already loaded (tests need this)
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if was_loaded:
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reload(module)
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self.migrated_apps.add(app_config.label)
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migration_names = {
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name for _, name, is_pkg in pkgutil.iter_modules(module.__path__)
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if not is_pkg and name[0] not in '_~'
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}
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# Load migrations
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for migration_name in migration_names:
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migration_path = '%s.%s' % (module_name, migration_name)
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try:
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migration_module = import_module(migration_path)
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except ImportError as e:
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if 'bad magic number' in str(e):
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raise ImportError(
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"Couldn't import %r as it appears to be a stale "
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".pyc file." % migration_path
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) from e
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else:
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raise
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if not hasattr(migration_module, "Migration"):
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raise BadMigrationError(
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"Migration %s in app %s has no Migration class" % (migration_name, app_config.label)
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)
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self.disk_migrations[app_config.label, migration_name] = migration_module.Migration(
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migration_name,
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app_config.label,
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)
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def get_migration(self, app_label, name_prefix):
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"""Return the named migration or raise NodeNotFoundError."""
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return self.graph.nodes[app_label, name_prefix]
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def get_migration_by_prefix(self, app_label, name_prefix):
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"""
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Return the migration(s) which match the given app label and name_prefix.
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"""
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# Do the search
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results = []
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for migration_app_label, migration_name in self.disk_migrations:
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if migration_app_label == app_label and migration_name.startswith(name_prefix):
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results.append((migration_app_label, migration_name))
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if len(results) > 1:
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raise AmbiguityError(
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"There is more than one migration for '%s' with the prefix '%s'" % (app_label, name_prefix)
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)
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elif not results:
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raise KeyError("There no migrations for '%s' with the prefix '%s'" % (app_label, name_prefix))
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else:
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return self.disk_migrations[results[0]]
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def check_key(self, key, current_app):
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if (key[1] != "__first__" and key[1] != "__latest__") or key in self.graph:
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return key
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# Special-case __first__, which means "the first migration" for
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# migrated apps, and is ignored for unmigrated apps. It allows
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# makemigrations to declare dependencies on apps before they even have
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# migrations.
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if key[0] == current_app:
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# Ignore __first__ references to the same app (#22325)
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return
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if key[0] in self.unmigrated_apps:
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# This app isn't migrated, but something depends on it.
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# The models will get auto-added into the state, though
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# so we're fine.
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return
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if key[0] in self.migrated_apps:
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try:
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if key[1] == "__first__":
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return self.graph.root_nodes(key[0])[0]
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else: # "__latest__"
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return self.graph.leaf_nodes(key[0])[0]
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except IndexError:
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if self.ignore_no_migrations:
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return None
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else:
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raise ValueError("Dependency on app with no migrations: %s" % key[0])
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raise ValueError("Dependency on unknown app: %s" % key[0])
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def add_internal_dependencies(self, key, migration):
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"""
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Internal dependencies need to be added first to ensure `__first__`
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dependencies find the correct root node.
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"""
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for parent in migration.dependencies:
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# Ignore __first__ references to the same app.
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if parent[0] == key[0] and parent[1] != '__first__':
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self.graph.add_dependency(migration, key, parent, skip_validation=True)
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def add_external_dependencies(self, key, migration):
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for parent in migration.dependencies:
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# Skip internal dependencies
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if key[0] == parent[0]:
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continue
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parent = self.check_key(parent, key[0])
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if parent is not None:
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self.graph.add_dependency(migration, key, parent, skip_validation=True)
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for child in migration.run_before:
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child = self.check_key(child, key[0])
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if child is not None:
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self.graph.add_dependency(migration, child, key, skip_validation=True)
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def build_graph(self):
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"""
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Build a migration dependency graph using both the disk and database.
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You'll need to rebuild the graph if you apply migrations. This isn't
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usually a problem as generally migration stuff runs in a one-shot process.
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"""
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# Load disk data
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self.load_disk()
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# Load database data
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if self.connection is None:
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self.applied_migrations = set()
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else:
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recorder = MigrationRecorder(self.connection)
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self.applied_migrations = recorder.applied_migrations()
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# To start, populate the migration graph with nodes for ALL migrations
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# and their dependencies. Also make note of replacing migrations at this step.
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self.graph = MigrationGraph()
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self.replacements = {}
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for key, migration in self.disk_migrations.items():
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self.graph.add_node(key, migration)
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# Internal (aka same-app) dependencies.
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self.add_internal_dependencies(key, migration)
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# Replacing migrations.
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if migration.replaces:
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self.replacements[key] = migration
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# Add external dependencies now that the internal ones have been resolved.
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for key, migration in self.disk_migrations.items():
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self.add_external_dependencies(key, migration)
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# Carry out replacements where possible.
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for key, migration in self.replacements.items():
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# Get applied status of each of this migration's replacement targets.
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applied_statuses = [(target in self.applied_migrations) for target in migration.replaces]
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# Ensure the replacing migration is only marked as applied if all of
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# its replacement targets are.
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if all(applied_statuses):
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self.applied_migrations.add(key)
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else:
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self.applied_migrations.discard(key)
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# A replacing migration can be used if either all or none of its
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# replacement targets have been applied.
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if all(applied_statuses) or (not any(applied_statuses)):
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self.graph.remove_replaced_nodes(key, migration.replaces)
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else:
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# This replacing migration cannot be used because it is partially applied.
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# Remove it from the graph and remap dependencies to it (#25945).
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self.graph.remove_replacement_node(key, migration.replaces)
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# Ensure the graph is consistent.
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try:
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self.graph.validate_consistency()
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except NodeNotFoundError as exc:
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# Check if the missing node could have been replaced by any squash
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# migration but wasn't because the squash migration was partially
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# applied before. In that case raise a more understandable exception
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# (#23556).
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# Get reverse replacements.
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reverse_replacements = {}
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for key, migration in self.replacements.items():
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for replaced in migration.replaces:
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reverse_replacements.setdefault(replaced, set()).add(key)
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# Try to reraise exception with more detail.
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if exc.node in reverse_replacements:
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candidates = reverse_replacements.get(exc.node, set())
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is_replaced = any(candidate in self.graph.nodes for candidate in candidates)
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if not is_replaced:
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tries = ', '.join('%s.%s' % c for c in candidates)
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raise NodeNotFoundError(
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"Migration {0} depends on nonexistent node ('{1}', '{2}'). "
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"Django tried to replace migration {1}.{2} with any of [{3}] "
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"but wasn't able to because some of the replaced migrations "
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"are already applied.".format(
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exc.origin, exc.node[0], exc.node[1], tries
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),
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exc.node
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) from exc
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raise exc
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def check_consistent_history(self, connection):
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"""
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Raise InconsistentMigrationHistory if any applied migrations have
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unapplied dependencies.
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"""
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recorder = MigrationRecorder(connection)
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applied = recorder.applied_migrations()
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for migration in applied:
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# If the migration is unknown, skip it.
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if migration not in self.graph.nodes:
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continue
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for parent in self.graph.node_map[migration].parents:
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if parent not in applied:
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# Skip unapplied squashed migrations that have all of their
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# `replaces` applied.
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if parent in self.replacements:
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if all(m in applied for m in self.replacements[parent].replaces):
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continue
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raise InconsistentMigrationHistory(
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"Migration {}.{} is applied before its dependency "
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"{}.{} on database '{}'.".format(
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migration[0], migration[1], parent[0], parent[1],
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connection.alias,
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)
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)
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def detect_conflicts(self):
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"""
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Look through the loaded graph and detect any conflicts - apps
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with more than one leaf migration. Return a dict of the app labels
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that conflict with the migration names that conflict.
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"""
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seen_apps = {}
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conflicting_apps = set()
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for app_label, migration_name in self.graph.leaf_nodes():
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if app_label in seen_apps:
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conflicting_apps.add(app_label)
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seen_apps.setdefault(app_label, set()).add(migration_name)
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return {app_label: seen_apps[app_label] for app_label in conflicting_apps}
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def project_state(self, nodes=None, at_end=True):
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"""
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Return a ProjectState object representing the most recent state
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that the loaded migrations represent.
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See graph.make_state() for the meaning of "nodes" and "at_end".
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"""
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return self.graph.make_state(nodes=nodes, at_end=at_end, real_apps=list(self.unmigrated_apps))
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