Batch method for adding a list of model instances
        to the db in one get_or_404.

        Args:

            models (list): A list of the instances to add.
            commit (bool, optional): Defaults to True. If False, the
                transaction won't get committed.
            check_type (bool, optional) :  If True, each instance
                is type checked and exception is thrown if it is
                not an instance of the model. By default, False.

        Returns:
            list: A list of `Model` instances

def add_all(cls, models, commit=True, check_type=False):
        """Batch method for adding a list of model instances
        to the db in one get_or_404.

        Args:

            models (list): A list of the instances to add.
            commit (bool, optional): Defaults to True. If False, the
                transaction won't get committed.
            check_type (bool, optional) :  If True, each instance
                is type checked and exception is thrown if it is
                not an instance of the model. By default, False.

        Returns:
            list: A list of `Model` instances

        """
        if check_type:
            for model in models:
                if not isinstance(model, cls):
                    raise ValueError('%s is not of type %s' (model, cls))
        if None in models:
            cls.session.add_all([m for m in models if m is not None])
        else:
            cls.session.add_all(models)
        try:
            if commit:
                cls.session.commit()
            return models
        except:
            cls.session.rollback()
            raise