144 lines
6.2 KiB
Python
144 lines
6.2 KiB
Python
import os
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from django.utils.importlib import import_module
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from django.utils.functional import cached_property
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from django.db.models.loading import cache
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from django.db.migrations.recorder import MigrationRecorder
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from django.db.migrations.graph import MigrationGraph
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from django.conf import settings
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class MigrationLoader(object):
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"""
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Loads 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 initialisation, 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):
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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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@classmethod
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def migrations_module(cls, app_label):
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if app_label in settings.MIGRATION_MODULES:
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return settings.MIGRATION_MODULES[app_label]
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app = cache.get_app(app_label)
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return ".".join(app.__name__.split(".")[:-1] + ["migrations"])
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def load_disk(self):
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"""
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Loads the migrations from all INSTALLED_APPS from disk.
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"""
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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 in cache.get_apps():
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# Get the migrations module directory
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app_label = app.__name__.split(".")[-2]
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module_name = self.migrations_module(app_label)
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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 "No module named" in str(e) and "migrations" in str(e):
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self.unmigrated_apps.add(app_label)
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continue
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self.migrated_apps.add(app_label)
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directory = os.path.dirname(module.__file__)
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# Scan for .py[c|o] files
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migration_names = set()
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for name in os.listdir(directory):
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if name.endswith(".py") or name.endswith(".pyc") or name.endswith(".pyo"):
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import_name = name.rsplit(".", 1)[0]
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if import_name[0] not in "_.~":
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migration_names.add(import_name)
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# Load them
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for migration_name in migration_names:
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migration_module = import_module("%s.%s" % (module_name, migration_name))
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if not hasattr(migration_module, "Migration"):
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raise BadMigrationError("Migration %s in app %s has no Migration class" % (migration_name, app_label))
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self.disk_migrations[app_label, migration_name] = migration_module.Migration(migration_name, app_label)
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@cached_property
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def graph(self):
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"""
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Builds a migration dependency graph using both the disk and database.
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"""
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# Make sure we have the disk data
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if self.disk_migrations is None:
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self.load_disk()
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# And the database data
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if self.applied_migrations is None:
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recorder = MigrationRecorder(self.connection)
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self.applied_migrations = recorder.applied_migrations()
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# Do a first pass to separate out replacing and non-replacing migrations
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normal = {}
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replacing = {}
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for key, migration in self.disk_migrations.items():
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if migration.replaces:
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replacing[key] = migration
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else:
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normal[key] = migration
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# Calculate reverse dependencies - i.e., for each migration, what depends on it?
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# This is just for dependency re-pointing when applying replacements,
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# so we ignore run_before here.
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reverse_dependencies = {}
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for key, migration in normal.items():
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for parent in migration.dependencies:
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reverse_dependencies.setdefault(parent, set()).add(key)
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# Carry out replacements if we can - that is, if all replaced migrations
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# are either unapplied or missing.
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for key, migration in replacing.items():
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# Do the check
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can_replace = True
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for target in migration.replaces:
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if target in self.applied_migrations:
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can_replace = False
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break
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if not can_replace:
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continue
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# Alright, time to replace. Step through the replaced migrations
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# and remove, repointing dependencies if needs be.
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for replaced in migration.replaces:
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if replaced in normal:
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del normal[replaced]
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for child_key in reverse_dependencies.get(replaced, set()):
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normal[child_key].dependencies.remove(replaced)
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normal[child_key].dependencies.append(key)
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normal[key] = migration
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# Finally, make a graph and load everything into it
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graph = MigrationGraph()
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for key, migration in normal.items():
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graph.add_node(key, migration)
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for key, migration in normal.items():
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for parent in migration.dependencies:
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graph.add_dependency(key, parent)
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return graph
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class BadMigrationError(Exception):
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"""
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Raised when there's a bad migration (unreadable/bad format/etc.)
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"""
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pass
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