A while back I was researching JSON document to document transforms. At this point I was frustrated, I was struggling to find any decent spec for performing these kind of transforms.

The good news is, I finally stumbled on a really nice library and spec called JSON-e. It has a really powerful syntax which is JSON based as well as a growing support for performing the transform in a number of languages (JavaScript, Python, Go, Rust).

If you are looking for an option for JSON document to document transforms and you stumble upon this article, take a look.