def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def has_commit(cls, location, rev):
        """
        Check if rev is a commit that is available in the local repository.
        """
        try:
            cls.run_command(
                ['rev-parse', '-q', '--verify', "sha^" + rev],
                cwd=location,
                log_failed_cmd=False,
            )
        except InstallationError:
            return False
        else:
            return True