One to many relation: retrieving documents with a single query

Returning to classic mongodb example (posts and users)开发者_如何学运维:

Posts:

{title: "Greetings", body:"Hello world", userId:12345}

Users:

{_id:12345, name:"John Smith", email:john@smith.org"}

How to get post

{title: "Greetings", body:"Hello world", <username>:"John Smith"}

with a sigle query?

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MongoDB is not an RDBMS - so NO JOINS - either you use two queries or you use embedding or you look at "database references".