mongodb: a query issue - node.js

Question

I am designing a MEAN (MongoDb + Express.js + Angular.js + Node.js) app.
The application actors are users and persons; currently there are ~1000 persons and ~100 users.
The users are the application registered users, and the persons are external people the users need to be informed of.
Each user is able to rate and take some notes about any person she is interested in.
The database schemas I'm planning are:
var person = new mongoose.Schema({
name: String,
phone: String,
...
};
var user = new mongoose.Schema({
name: String,
email: String,
...
},
var userToPersonSchema = new mongoose.Schema({
userId: { type: ObjectId , required: true },
personId: { type: ObjectId, required: true },
rating: Number,
notes: String,
...
});
This is the query I plan to add user rating for a person:
db.userToPerson.insert({
userId: currentUserId,
personId: currentPersonId,
rating: 10,
notes: 'my preferred person!'
});
This is the code I have to find all persons with a rating by a user:
var currentUserId = '123...';
var personsAll = db.person.find();
var usersToPersonsAll = db.userToPerson.find({ _id: currentUserId });
var personsRatedByCurrentUser = [];
for (var p = 0; p < personsAll.length; p++) {
for (var u = 0; u < usersToPersonsAll.length; u++) {
if (personsAll[p]._id === usersToPersonsAll[u].personId) {
personsRatedByCurrentUser.push(personsAll[p]);
}
}
}
The question:
for the last "query" I suppose I'd better use some form of aggregation, but I can't find out any...
Any advise about a schema design modification should be welcome, too, of course...

Answer 1

Any time I need a join in MongoDB, I break the problem into two queries.
First, fetch the ids from the first collection using distinct. Distinct just returns an array of unique values.
Then, query the second collection for documents corresponding to those ids. The $in parameter conveniently takes an array.
var currentUserId = '123...';
var personIds = db.userToPerson.distinct("personId", { _id: currentUserId });
var personsRatedByCurrentUser = db.person.find({ _id: {$in, personIds}});