def get_model_field(schema, field):
    """Get the model field of a schema field

    :param Schema schema: a marshmallow schema
    :param str field: the name of the schema field
    :return str: the name of the field in the model
    """
    if schema._declared_fields.get(field) is None:
        raise Exception('{} has no attribute {}'.format(schema.__name__, field)
            )
    if schema._declared_fields[field].attribute is not None:
        return schema._declared_fields[field].attribute
    return field
