Mongoose Schema populate array field from another collection

Question

I have two collections questions and answers which look like this.

question:

{ 
"_id" : ObjectId("56a450880c9a072eb092774f"), 
"text" : "Who are you?"
}

answer:

{ 
"_id" : ObjectId("56a452930c9a072eb092775f"), 
"text" : "I'm me!", 
"correct" : true, 
"question_id" : ObjectId("56a450880c9a072eb092774f")
}

and then I have two Schemas :

AnswerSchema:

var answerSchema = new Schema({
answer: String,
correct: Boolean,
question_id : {type: db.Schema.Types.ObjectId, ref: 'Question'}
});

QuestionSchema

var  questionSchema = new Schema({
text: String,
answers : [answerSchema]
});

So basically, I want to query the data base to spit a json like this where the answers get populated:

{
_id: "56a451150c9a072eb0927751",
text: "Who are you?",
answers: [
  { "answer" : "I'm me!", "correct": true },
  { "answer" : "I'm you!", "correct": false },
  { "answer" : "You are you", "correct": false }
]}

I can query the questions but the answers are not populated by doing this:

    Question.find({})
    .populate("answers")
    .exec(function (err, questions) {
        //if(err) res.status(500).send(err);
        //else res.json(questions);
        res.json(questions);
});

How can I achieve what I'm trying to do. Thanks.

zangw · Accepted Answer · 2016-01-24 08:30:52Z

1

Since the answerSchema is the sub-document of QuestionSchema

var questionSchema = new Schema({
   text: String,
   answers : [answerSchema]
});

To meet your requirement, it is easy to do with

Question.find({})
    .exec(function (err, questions) {
        // all answers are in the every question as sub-document.
});

As for populate, when you want to

Question.find({})
  .populate("answers")
  .exec(function (err, questions) {
     //....
});

The questionSchema and answerSchema should be

var answerSchema = new Schema({
  answer: String,
  correct: Boolean
});
var Answer = mongoose.model("Answer", answerSchema);

var questionSchema = new Schema({
  text: String,
  answers : [{type: db.Schema.Types.ObjectId, ref: 'Answer'}]
});

answered Jan 24, 2016 at 8:30

zangw

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