MongoDB, Mongoose: How to find subdocument in found document?

Question

I\'m stuck on trying to get subdocument by _id in found document.

Example Schema

var User = mongoose.Schema({
        name:       String         


        

Answer 1

Adding to srquinn's answer, from my limited experience I thought populate was for joining documents from different collections together?

I think here you could just do User.findOne({ name: 'foo' }, 'photos') which is shorthand for:

const query = User.findOne({ name: 'foo' })
query.select('photos')

Answer 2

You need to either create a NEW Schema for your embedded documents, or leave the type declaration as a blank array so mongoose interprets as a Mixed type.

var userSchema = new mongoose.Schema({
  name: String,
  photos: []
});
var User = mongoose.model('User', userSchema);

-- OR --

var userSchema = new mongoose.Schema({
  name: String,
  photos: [photoSchema]
});

var photoSchema = new mongoose.Schema({
  src: String,
  title: String
});

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

And then you can save thusly:

var user = new User({
  name: 'Bob',
  photos: [ { src: '/path/to/photo.png' }, { src: '/path/to/other/photo.png' } ]
});

user.save();

From here, you can simply use array primitives to find your embedded docs:

User.findOne({name: 'Bob'}, function (err, user) {

  var photo = user.photos.filter(function (photo) {
    return photo.title === 'My awesome photo';
  }).pop();

  console.log(photo); //logs { src: '/path/to/photo.png', title: 'My awesome photo' }
});

-- OR --

You can use the special id() method in embedded docs to look up by id:

User.findOne({name: 'Bob'}, function (err, user) {
    user.photos.id(photo._id);
});

You can read more here: http://mongoosejs.com/docs/subdocs.html

Make sure you DON'T register the schema with mongoose, otherwise it will create a new collection. Also keep in mind that if the child documents are searched for often, it would be a good idea to use refs and population like below. Even though it hits the DB twice, its much faster because of indexing. Also, mongoose will bonk on double nesting docs (i.e. The children have children docs as well)

var user = mongoose.Schema({
  name: String,
  photos: [{ type: Schema.Types.ObjectId, ref: 'Photo' }]
});

var photo = mongoose.Schema({
  src: String,
  title: String
});

User
  .findOne({ name: 'foo' })
  .populate('photos')
  .exec(function (err, user) {
    console.log(user.photos[0].src);
  });

Relevant docs can be found here http://mongoosejs.com/docs/populate.html