move collection from A_db to B_db

- query

use A
db.A_COLLECTION_NAME.find().forEach(function(row)
	{ db.getSiblingDB('B_DB')['B_COLLECTION_NAME'].insert(row); }
);

- shell

$ mongodump -d A -c A_COLLECTION_NAME
$ mongorestore -d B -c B_COLLECTION_NAME /dump/some_collection.bson