Unique index validation error not throwing

I’m using this schema with latest npm mongoose:

var schema = new Schema({

    _id: Schema.ObjectId,
    email: {type: String, required: true, unique: true}

});

If I try to save a email that is already in db, I expect to get a ValidationError like if a required field is omitted. However this is not the case, I get a MongoError: E11000 duplicate key error index.

Which is not a validation error (happens even if I remove the unique:true).

[blakehaswell]

For anyone interested, I’ve added a plugin which checks the DB prior to saving and throws a Mongoose validation error if any of your unique constraints will be violated: https://github.com/blakehaswell/mongoose-unique-validator

[lukejacksonn]

I had this issue and it was due to already existing duplicate values in my index (as pointed out in aheckmann’s comment on Feb 1, 2013). I was reading from here http://mongoosejs.com/docs/api.html#schematype_SchemaType-required where it mentions the error, but fails to mention about already exiting duplicates preventing the uniques index from being created in the first place. Might be worth updating the doc to mention this too!