def init_db(self, txn=None):
        """Connect to database and create tables.

        Parameters
        ----------
        txn : sa.engine.Connection, optional
            The transaction to execute in. If this is not provided, a new
            transaction will be started with the engine provided.

        Returns
        -------
        metadata : sa.MetaData
            The metadata that describes the new assets db.
        """
        with ExitStack() as stack:
            if txn is None:
                txn = stack.enter_context(self.engine.begin())

            tables_already_exist = self._all_tables_present(txn)

            # Create the SQL tables if they do not already exist.
            metadata.create_all(txn, checkfirst=True)

            if tables_already_exist:
                check_version_info(txn, version_info, ASSET_DB_VERSION)
            else:
                write_version_info(txn, version_info, ASSET_DB_VERSION)
Connect to database and create tables.

        Parameters
        ----------
        txn : sa.engine.Connection, optional
            The transaction to execute in. If this is not provided, a new
            transaction will be started with the engine provided.

        Returns
        -------
        metadata : sa.MetaData
            The metadata that describes the new assets db.