Question

Suppose I have a user Schema as below

var User = new db.Schema({
    username    : {type: String, unique: true}
    , password    : String
    , email: String
});

To accommodate the user having friends I’m thinking of modifying the schema as follows

var User = new db.Schema({
    username    : {type: String, unique: true}
    , password    : String
    , email: String
    , friends: [?]
});

Rather than just storing ObjectIds I’m thinking of denormalizing the database for faster queries. Suppose for now I just wish to store ObjectId and username in the friends array. Is it possible to do something like

friends: [{String, String}]

where the two Strings represent ObjectId and username? I don’t want to create a brand new schema since I don’t need a new ObjectId.

Answer 1

Sure you can do this, but I would really advice to name the fields, like (in Mongo shell syntax):

user = {
    '_id' : ObjectId(....),
    'username' : 'derick',
    'password' : 'notmypw',
    'email' : '[e-mail]',
    'friends' : [
        { 'id': ObjectId(....), 'username' : 'adam' },
        { 'id': ObjectId(....), 'username' : 'ross' },
    ]
};

However, you (of course) don’t have to store the ObjectId at all, as your username is already unique. Heck, you could even make a user’s username as ID for the _id field:

user = {
    '_id' : 'derick',
    'password' : 'notmypw',
    'email' : '[e-mail]',
    'friends' : [
        { 'username' : 'adam' },
        { 'username' : 'ross' },
    ]
};

I think in Mongoose, you’ll have to do this like (from reading “Defining documents within documents” at http://mongoosejs.com/docs/model-definition.html)

var Friend = new db.Schema({
    username  : String
});

var User = new db.Schema({
    username    : {type: String, unique: true}
    , password    : String
    , email: String
    , friends: [Friend]
});