Unique Constraint with Two Fields in MongoDB

Question

I have a collection with fields \"email\" and \"friends_email\". I would like to setup a unique-ness constraint like the following, using MongoDB:

1. No record

Answer 1

It sounds like you need a compound unique index:

db.users.createIndex( { "email": 1, "friends_email": 1 }, { unique: true } )

... and you can verify at the ORM layer that email =/= friends_email.

Answer 2

for the second case, is a unique compound index what you're looking for?

 db.emails.ensureIndex( {email:1, friends_email:1}, { unique: true } )

As for the first case, I am not sure if there is a way to enforce the first rule. You may need to perform the check on the application side.

Answer 3

You can have compound unique index on email and friends_email field for ensuring the second case. But for the first case you need to handle that in the application code or use a java mapper such as Morphia to have a field-based validation. You might wanna check the following post also:

How to apply constraints in MongoDB?