Question

I have documents in a collection that have an array of properties (1-400 different numeric values).

Now i want to get all documents of another collection that have one of these properties (these documents only have one property).

How can i do that, preferably in one call?

Answer 1

As MongoDB is no relational DBMS this isn’t possible to achieve with only one call.
What you need to do is to first retrieve your document your want to use for your search. Upon you retrieved it, you’re using that array stored in the document todo a $in query on the field for the other collection. So for the mongo shell this could be something like this:

var ar = db.coll1.findOne().numArray
db.coll2.find({b: { $in : ar }})