error retrieving records using object id , error : INVALID OBJECT ID

[bhaskar rao]

Hai , lets say i have two collections users and colleges

users collection have
_id , username .

I want to add some users to colleges collection .
Should i add _id or username or some normal id(that increments when
inserted new row) to the colleges collection for reference .What gives
BETTER PERFORMANCE ?

I heard that _id (object id) gives better performance .

So i tried using that .

But when i tried to retrive records using _id like this :

Model.find({ _id : "idstring" })

it is giving error "invalid object id"

i am not getting error when retrieving using others like username

Whats the solution ?

Thanks .

[gregor]

Are you using ObjectId("string") ?

http://www.mongodb.org/display/DOCS/Object+IDs#ObjectIDs-TheBSONObjectIdDatatype

Using the _id as a reference in your colleges collection will give better performance than your own counter but also you could consider embedding some of the user data in the college document - mongo is not a denormalized db and so supports this. 

Take a look at schema design

http://www.mongodb.org/display/DOCS/Schema+Design