Class MigrationLoader

django/db/migrations/loader.py:21–433

Load migration files from disk and their status from the database. Migration files are expected to live in the "migrations" directory of an app. Their names are entirely unimportant from a code perspective, but will probably follow the 1234_name.py convention. On initializatio

class MigrationLoader:
    """
    Load migration files from disk and their status from the database.

    Migration files are expected to live in the "migrations" directory of
    an app. Their names are entirely unimportant from a code perspective,
    but will probably follow the 1234_name.py convention.

    On initialization, this class will scan those directories, and open and
    read the Python files, looking for a class called Migration, which should
    inherit from django.db.migrations.Migration. See
    django.db.migrations.migration for what that looks like.

    Some migrations will be marked as "replacing" another set of migrations.
    These are loaded into a separate set of migrations away from the main ones.
    If all the migrations they replace are either unapplied or missing from
    disk, then they are injected into the main set, replacing the named
    migrations. Any dependency pointers to the replaced migrations are
    re-pointed to the new migration.

    This does mean that this class MUST also talk to the database as well as
    to disk, but this is probably fine. We're already not just operating
    in memory.
    """

    def __init__(
        self,
        connection,
        load=True,
        ignore_no_migrations=False,
        replace_migrations=True,
    ):
        self.connection = connection
        self.disk_migrations = None
        self.applied_migrations = None
        self.ignore_no_migrations = ignore_no_migrations
        self.replace_migrations = replace_migrations
        if load:
            self.build_graph()

    @classmethod
    def migrations_module(cls, app_label):
        """
        Return the path to the migrations module for the specified app_label
        and a boolean indicating if the module is specified in
        settings.MIGRATION_MODULE.
        """
        if app_label in settings.MIGRATION_MODULES:
            return settings.MIGRATION_MODULES[app_label], True
        else:
            app_package_name = apps.get_app_config(app_label).name
            return "%s.%s" % (app_package_name, MIGRATIONS_MODULE_NAME), False

    def load_disk(self):
        """Load the migrations from all INSTALLED_APPS from disk."""
        self.disk_migrations = {}
        self.unmigrated_apps = set()
        self.migrated_apps = set()