code: def get_instance_by_slug(model, slug, **kwargs):
      
      try:
          model = get_model(model)
      except ImportError:
          return None
  
      query_params = dict(kwargs)
      query_params['slug'] = slug
  
      return model.query.filter_by(**query_params).first()
docs: Get an instance by slug.
  
      :param model: a string, model name in rio.models
      :param slug: a string used to query by `slug`. This requires there is a
                   slug field in model definition.
      :return: None or a SQLAlchemy Model instance.