generator to return the tuple of model and its schema to create on aws.

def models(self):
        '''
        generator to return the tuple of model and its schema to create on aws.
        '''
        model_dict = self._build_all_dependencies()
        while True:
            model = self._get_model_without_dependencies(model_dict)
            if not model:
                break
            yield (model, self._models().get(model))