sql.py 文件源码

def sql_delete(app_config, style, connection, close_connection=True):
    "Returns a list of the DROP TABLE SQL statements for the given app."

    check_for_migrations(app_config, connection)

    # This should work even if a connection isn't available
    try:
        cursor = connection.cursor()
    except Exception:
        cursor = None

    try:
        # Figure out which tables already exist
        if cursor:
            table_names = connection.introspection.table_names(cursor)
        else:
            table_names = []

        output = []

        # Output DROP TABLE statements for standard application tables.
        to_delete = set()

        references_to_delete = {}
        app_models = router.get_migratable_models(app_config, connection.alias, include_auto_created=True)
        for model in app_models:
            if cursor and connection.introspection.table_name_converter(model._meta.db_table) in table_names:
                # The table exists, so it needs to be dropped
                opts = model._meta
                for f in opts.local_fields:
                    if f.rel and f.rel.to not in to_delete:
                        references_to_delete.setdefault(f.rel.to, []).append((model, f))

                to_delete.add(model)

        for model in app_models:
            if connection.introspection.table_name_converter(model._meta.db_table) in table_names:
                output.extend(connection.creation.sql_destroy_model(model, references_to_delete, style))
    finally:
        # Close database connection explicitly, in case this output is being piped
        # directly into a database client, to avoid locking issues.
        if cursor and close_connection:
            cursor.close()
            connection.close()

    if not output:
        output.append('-- App creates no tables in the database. Nothing to do.')
    return output[::-1]  # Reverse it, to deal with table dependencies.