say you have a model with two attributes profile_image_url: str and profile_image: bytes
it's expensive to fetch profile_image since it will involve a http call to profile_image_url. right now, i would resolve this by using the @property decorator
this library offers an alternative method for populating profile_image by explicitly giving the user a hook for when they want to resolve this dependency. they might want to do it before access time, they might want to batch requests to this external profile_image service to reduce roundtrip latency
this pattern has potential to become more powerful if we only have user_id in context initially. we might want to fetch the product_image_url from the database then fetch the actual product_image after. this dependency graph might be simplified/optimized using this tool
the repo provides its own concrete example of this form with batch_person_age_loader
