MongoDB: Combine data from multiple collections into one..how?

Question

How can I (in MongoDB) combine data from multiple collections into one collection?

Can I use map-reduce and if so then how?

I would greatly appreciate some

Answer 1

You've to do that in your application layer. If you're using an ORM, it could use annotations (or something similar) to pull references that exist in other collections. I only have worked with Morphia, and the @Reference annotation fetches the referenced entity when queried, so I am able to avoid doing it myself in the code.