def register_model_serializer(model):
    """
        Registers the serializer with a given model.
        Throws an exception, if the model already has an instance_serializer_class field associated to it.
    """
    def register_serializer(serializer_class):
        assert not hasattr(model, 'instance_serializer_class') or model.instance_serializer_class == serializer_class

        model.instance_serializer_class = serializer_class
        return serializer_class
    
    return register_serializer