how to search two collections based on some condition

how to search two collections based on some condition

Exampe :
collectionA

{ code:"test",name:"sample" }

collectionb

{ code:"test2",name:"sample2" }

collectionc

{ code:"test",name:"sample2" }

check the code:"test" in all collections.

MongoDB only ever searches one collection per query. Searching three collections requires three queries to the database.

    > db.collectionA.find({ "code" : "test" })

    > db.collectionB.find({ "code" : "test" })

    > db.collectionC.find({ "code" : "test" })

You can use Map reduce function for this..

Actually no, you can't.  MapReduce, like all other operations in MongoDB only runs on a single collection per invocation.

Will is correct - it's just three queries, one against each collection.