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

If there is no bulk insert into mongodb, we loop all objects in the small_collection and insert them one by one into the big_collection:

db.small_collection.find().forEach(function(obj){ 
   db.big_collection.insert(obj)
});