Populate subdocument in parent document Array Mongoose

Question

I'm very new to JavaScript and Mongoose. I'm building a small project using express, mongoose and node.js. I have a mongoose model - Client that has an Array of Transactions

    var Client = mongoose.model('Client', {
 name: {
   type: String,
   required: true,
   minlength: 1
 },
 email: {
   type: String
 },
 phone: {
   type: Number
 },
 createdAt: {
   type: Number,
   default: null
 },
 transactions: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Transaction' }],
 _creator: {
   type: mongoose.Schema.Types.ObjectId,
   required: true
 }
});

module.exports = {Client};

This is Transaction model:

var Client = require('./client');

var Transaction = mongoose.model('Transaction',{
  _creator : { type: mongoose.Schema.Types.ObjectId, ref: 'Client' },
  amount : {type: Number, min: 0},
  date : {type: Number,default: null},
  total: {type: Number,default: null}
});

module.exports = {Transaction};

When I POST a new Transaction it goes through and saves in db:

 app.post('/clients/:id/transactions', authenticate, (req, res) => {
  var id = req.params.id;
  var transaction = new Transaction({
    amount: req.body.amount,
    date: new Date().getTime(),
    total: req.body.total,
    _creator: req.params.id
  })
  if (!ObjectID.isValid(id)) {
  return res.status(404).send();
  }

  transaction.save().then((doc) => {

    Client.findOneAndUpdate({
      _id: id,
      _creator: req.user._id,
      transactions: req.body.transaction
    });

    res.send(doc);
  }, (e) => {
    res.status(400).send(e);
  });

});

I am also able to GET all the transactions associated with the client:

  app.get('/clients/:id/transactions', authenticate, (req, res) => {
  var id = req.params.id;
  if (!ObjectID.isValid(id)) {
  return res.status(404).send();
 }
 Transaction.find({
   _creator: id
 }).then((transactions) => {
  res.send({transactions});
 }).catch((e) => {
  res.status(400).send();
 });
});

But when I make a GET call to '/clients' - Array of Transactions is empty:

    {
  "clients": [
    {
      "_id": "1095d6de3867001108b803",
      "name": "Peter",
      "email": "peter@gmail.com",
      "phone": 1232321,
      "_creator": "5321df6d57868ec7001108b801",
      "__v": 0,
      "transactions": [],
      "createdAt": null
    } ]
}

And this is the GET call to /clients

    app.get('/clients', authenticate,  (req, res) => {
  Client.find({
    _creator: req.user._id,
  })
  .populate('transactions.transaction')
  .then((clients) => {
    res.send({clients});
  }, (e) => {
    res.status(400).send(e);
    console.log('Unable to get clients', e);
  })
});

I know that I'm likely doing something completely wrong but I don't know where I need to look for my mistake. Please help!

Answer 1

so first of all i don't exactly know what _creator key in Client model representing, it's probably user identifier who has some clients, but if I'm wrong please correct me.

Honestly I don't know why you are making two way document connection, (keeping client in transactions, and also keeping transactions in clients) in my opinion first option is better for mongodb and using that you can easily get transaction's list with find, or mongodb aggregation, but you can't get data using populate .

In second option you need to remember that one document could have maximum 16MB. And also keeping thousands of transactions in one array is not well for performance. Think about example that you have 5000 transaction and you want to show list with pagination (50 records per page), with array option you have to get whole document, and splice array to 50 records. In first option you could use mongodb skip and limit. Please think about it.

Returning to question, mistake you are doing is here: transaction.save().then((doc) => {

Client.findOneAndUpdate({
  _id: id,
  _creator: req.user._id,
  transactions: req.body.transaction
});

res.send(doc);

Here you don't exactly say how this document should have to updated about.

Mongoose in method findOneAndUpdate using mongodb findAndModify method. But params are used from update. https://docs.mongodb.com/manual/reference/method/db.collection.update/

And also documentation says that you what params like: Query#findOneAndUpdate([query], [doc], [options], [options.passRawResult], [options.strict], [callback])

So first query param is mongo query to find one document in database, next param is object with updating query, and after that you could send some additional options in third param. So your code should looks like this:

transaction.save().then((doc) => {

Client.findOneAndUpdate({
  _id: id,
  _creator: req.user._id,
}, {
    $addToSet:  {
        transactions: doc._id,
    }
});

res.send(doc);

You could use addToSet or push both are putting element into array, but addToSet avoiding duplicates in array. And as you se we push new transaction identifier into this array. And after all you only populate transaction key.

I hope I helped. If you have any questions please ask.

Answer 2

I would check if the client exist before adding a transaction. A transaction needs a client first.

Forewarn, I'm not a fan of then and catch so this answer does not use it. I normally use async.js when dealing with multiple asynchronous operations.

Anyways, I would do it like

app.post('/clients/:id/transactions', authenticate, (req, res) => {


    Client.findOne({ _id: req.params.id }, (err, client) => {
        if (err)
            return res.status(400).send(err); 
        if (!client)
            return res.status(400).send(new Error('No client'));


        Transaction.create({
            amount: req.body.amount,
            date: new Date(), // I don't think you need .getTime()
            total: req.body.total,
            _creator: client._id
        }, (err, transaction) => {
            if (err)
                return res.status(400).send(err);


            client.transactions.push(transaction._id);
            client.save(err => {
                if (err)
                    return res.status(400).send(err);

                res.json(transaction);
            });
        });
    });


});

Good idea to also turn on debugging mode to see your queries: mongoose.set('debug', true) .

You might also find using timestamps option for Transaction schema more useful than explicitly using date field

To get clients with their transactions

app.get('/clients', authenticate,  (req, res) => {
    Client.find({ _creator: req.user._id }).populate('transactions').exec((err, clients) => {
        if (err)
            return res.status(400).send(err);
        res.json(clients);
    });
});