Question

I have a schema for an item and a user. I want to allow a user to like or dislike an item and I also want to store a ratings association on the item as well as the user.

var UserSchema = new Schema({
    username    : { type: String, required: true, index: { unique: true }
   , likes : [{ type: Schema.ObjectId, ref: 'Item'}]
   , dislikes : [{ type: Schema.ObjectId, ref: 'Item'}]
   , ratings: [???]
});

var ItemSchema = new Schema({
    name: { type: String},
   , likes : [{ type: Schema.ObjectId, ref: 'User'}]
   , dislikes : [{ type: Schema.ObjectId, ref: 'User'}]
   , ratings: [???]
});

The user stores an item ref, and the item stores a user ref for likes/dislikes. I am not sure how to store ratings for as an attribute though, since I want both the user and the value they rated the item.

item.ratings.forEach(function(rating){
  <%= rating.user.username %> gave <%= item.name %> a <%= rating.value %>.
});

I also want to get a list of items a user has rated along with the rating value:

user.ratings.forEach(function(rating){
  <%= user.username %> has rated <%= rating.item.name %> and gave it a <%= rating.value %>
});

What should my “ratings” schema look like? Is it possible to store two values? a user object id and a rating value (integer) and have a collection of these?

The other problem I see with my method is that mongoose doesn’t support deep populate yet, so I would have to either use a module for it (https://github.com/JoshuaGross/mongoose-subpopulate), that is largely un-tested or store it in a different manner that won’t have more than one level of nesting, so I can get my data with .populate()

Any feedback is appreciated, as I’m new to noSQL and perhaps I’m overcomplicating this.

Answer 1

I would do as you said. I would use a Rating schema:

var RatingSchema = new Schema({
   , _user : { type: ObjectId, ref: 'User' }
   , _item : { type: ObjectId, ref: 'Item' }
   , value : Integer
});

If you want to be able to access the ratings from the User schema, you would have to add a hook so that any saved RatingSchema is added to user.ratings.

var UserSchema = new Schema({
  /* ... */
  ratings: [{ type: Schema.ObjectId, ref: 'Rating'}]
});

RatingSchema.post('save', function () {
  // push this.id to this._user.ratings
  // save this._user
});

Regarding, “The other problem I see with my method is that mongoose doesn’t support deep populate yet”, if you don’t want to use the mongoose-subpopulate hack, I suggest you refactor the loading of your models into static methods. For example:

UserSchema.statics.findByIdAndDeepPopulate = function (i, cb) {
  UserSchema.findOne(id)
    .exec(function(err, user) {
      if (err || !user) return cb(new Error('User not found'));
      if (user._ratings.length == 0) return cb(null, user);

      // Load and populate every ratings in user._ratings
      for(var i = 0; i < user._ratings.length; i++) {
        function(i) {
          RatingSchema
            .populate('_item')
            .exec(err, function(rating) {
              user._ratings[i] = rating;
              if (i == user._ratings.length) return cb(null, user);
            });
        }(i);
      }
    });
}

EDIT: Now that I think about it again, why not simply store the ratings as an embed document in UserSchema?

var UserSchema = new Schema({
  /* ... */
  ratings: [ RatingSchema ]
});

You could then simply populate this way:

UserSchema.findOne(id)
  .populate('ratings._item')
  .exec(function(err, user) {
    if (err || !user) return next(new Error('User not found'));

    console.log(user.ratings);
  });