How to find a sub-document using Mongoose?

Question

I'm trying to get a sub-document in my User collection using mongoose. I followed the Mongoose Sub Document on its official website. It's written that:

Each document has an _id. DocumentArrays have a special id method for looking up a document by its _id.

var doc = parent.children.id(id);

Here is my code:

exports.editAccount = function(req, res) {
    var user = new User(req.user);
    var newAccount = new Account(req.body);
    console.log("Account:" + newAccount._id); // Gave me 53bf93d518254f880c000009
    var account = user.accounts.id(newAccount._id);
    console.log("Account" + account); // Never been printed
};

The console.log("Account" + account); has never been printed. I don't know what happen. I tried many different ways, however, still can't figure it out. Any help would be appreciated.

---

User collection:

{
    "__v" : 1,
    "_id" : ObjectId("53bcf3e6fbf5adf10c000001"),
    "accounts" : [
        {
            "accountId" : "123456789",
            "type" : "Saving account",
            "balance" : 100,
            "_id" : ObjectId("53bf93d518254f880c000009")
        }
    ]
}

I

Answer 1

Not too sure how you have defined your Schema or basically even model instances, but really all you need is this:

var accountSchema = new Schema({
    "accountId": String,
    "type": { "type": String, "enum": ["Saving Account", "Checking Account"] },
    "balance": { "type": Number, "default": 0 }
]);

var userSchema = new Schema({
    "accounts": [accountSchema]
]);

var User = mongoose.model( "User", userSchema );

Then when you want to add an account to the User you just do, presuming you have input that matches the first variable declaration:

var input = {
    "accountId": "123456789",
    "type": "Savings Account",
};

User.findByIdAndUpdate(
    userId,
    { "$push": { "accounts": input } },
    function(err,user) {
        // work with result in here
    }
);

That does bypass things like validation and other hooks, but is more efficient in communicating with MongoDB.

If you really need the validation and/or other features then you and using a .find() variant and issuing a .save() method.

User.findById(userId,function(err,user) {
    if (err) throw err;    // or handle better

    user.accounts.push( input );
    user.save(function(err, user) {
        // more handling
    });
]);

And to modify the document then you are doing much the same. Either by the most efficient MongoDB way:

var input = {
    accountId: "123456789",
    amount: 100
};

User.findOneAndUpdate(
    { "_id": userId, "accounts.accountId": input.accountId },
    { "$inc": { "accounts.$.balance": input.amount } },
    function(err,user) {
        // handle result
    }
);

Or again where you need the Mongoose hooks and or validation to apply:

User.findById(userId,function(err,user) {
    if (err) throw err;   // or handle otherwise

    user.accounts.forEach(function(account) {
        if ( account.accountId === input.accountId )
            account.balance += input.balance;
    });

    user.save(function(err,user) {
        // handle things
    });
);

Remember that these things are "arrays", and you can either handle them the MongoDB way or the JavaScript way. It just depends on where you choose to "validate" your input.

---

More code to illustrate where the usage is not correct:

var async = require('async'),
    mongoose = require('mongoose'),
    Schema = mongoose.Schema;

mongoose.connect('mongodb://localhost/child');


var accountSchema = new Schema({
  "accountId": String,
  "type": { "type": String },
  "balance": { "type": Number, "default": 0 }
});

var userSchema = new Schema({
  "accounts": [accountSchema]
});

var User = mongoose.model( "User", userSchema );

async.waterfall([

  function(callback) {
    User.create({},function(err,user) {
      if (err) throw err;
      console.log(
        "Created:\n%s\n",
        JSON.stringify( user, undefined, 4 )
      );
      callback(null,user);
    });
  },

  function(user,callback) {
    var account = user.accounts.create({
      "accountId": "123456789",
      "type": "Savings"
    });

    console.log(
      "Account is:\n%s\n",
      JSON.stringify( account, undefined, 4 )
    );

    console.log(
      "User is still:\n%s\n",
      JSON.stringify( user, undefined, 4 )
    );

    user.accounts.push( account );

    console.log(
      "User Changed:\n%s\n",
      JSON.stringify( user, undefined, 4 )
    );

    User.findById(user.id,function(err,saved) {
      if (err) throw err;
      console.log(
        "Persisted is still:\n%s\n",
        saved
      );
      user.save(function(err,user) {
        if (err) throw err;
        callback(null,user,account);
      });
    });

  },

  function(user,account,callback) {

    User.findById(user.id,function(err,saved) {
      if (err) throw err;
      console.log(
        "Persisted is now:\n%s\n",
        saved
      );

      var item = user.accounts.id(account.id);
      console.log(
        "Item is:\n%s\n",
        item
      );
      callback();
    });
  }
],function(err) {
  process.exit();
});

Results:

Created:
{
    "__v": 0,
    "_id": "53c08ab51083d1fe3852becc",
    "accounts": []
}

Account is:
{
    "accountId": "123456789",
    "type": "Savings",
    "_id": "53c08ab51083d1fe3852becd",
    "balance": 0
}

User is still:
{
    "__v": 0,
    "_id": "53c08ab51083d1fe3852becc",
    "accounts": []
}

User Changed: 
{
    "__v": 0,
    "_id": "53c08ab51083d1fe3852becc",
    "accounts": [
        {
            "accountId": "123456789",
            "type": "Savings",
            "_id": "53c08ab51083d1fe3852becd",
            "balance": 0
        }
    ]
}

Persisted is still:
{ _id: 53c08ab51083d1fe3852becc, __v: 0, accounts: [] }

Persisted is now:
{ _id: 53c08ab51083d1fe3852becc,
  __v: 1,
  accounts:
  [ { accountId: '123456789',
      type: 'Savings',
      _id: 53c08ab51083d1fe3852becd,
      balance: 0 } ] }

Item is:
{ accountId: '123456789',
  type: 'Savings',
  _id: 53c08ab51083d1fe3852becd,
  balance: 0 }