java mongo custom object id userid

Question

We have a User doc in Mongo DB and want to use the _id field as the userID field and increment it.
i found a counter("user") JS method in Mongo docs (http://www.mongodb.org/display/DOCS/Object+IDs).

From the Mongo Shell, i can invoke,

db.user.insert({_id:counter("user"), name:"tom"...});

Now, how can i use the same command from Java code? Not able to find a way to specify the Javascript function from Java code.
Also saw the findAndModify Command and usage of $inc, but not able to get it to work. This way we can do without invoking the JS counter func, i presume.

What are the implications of using custom value in the _id field instead of the Mongo's Object Id, any caveats?
~vish

Why do you want to increment it? Why not generate totally new ObjectId? — Sergio Tulentsev, Jul 30 '12 at 06:08
i can use the ObjectID's in the Java code, but tomorrow if they want to change the DB to something else, is it ok to still be referring to ObjectId's for the ids like userID, roleID, permissionID etc..i don't know about it, please advise. — Blue Sky, Jul 30 '12 at 06:13
You will have bigger problems if they decide to change database later. Just use ObjectIds. — Sergio Tulentsev, Jul 30 '12 at 06:16
Thanks, i will go ahead with ObjectID's for the ids in diff tables(docs). — Blue Sky, Jul 30 '12 at 06:17
So for display purposes, i can convert the ObjectId to a string representation, isn't it?. toString() might work..i think — Blue Sky, Jul 30 '12 at 06:20

score 0 · Accepted Answer · answered Jul 30 '12 at 06:26

TL;DR: Just use ObjectIds

It makes little sense to generate new ObjectIds like that. You should just create a new ObjectId for each new object. It's easy and offers good global uniqueness guarantees.

If you're doing this to abstract yourself from the database, it won't work. MongoDB is a very specific database. Abstraction is possible if you only use mongo as a K/V store (think memcached, but slower), but there are better products with this functionality.

java mongo custom object id userid

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