Partial update of a subdocument with nodejs/mongoose

Question

Is it possible to set multiple properties on a (sub)document in one go with Mongoose? An example of what I'm trying to do:

Let's say I have this schema:

var subSchema = new Schema({
    someField: String,
    someOtherField: String
});

var parentSchema = new Schema({
    fieldOne: String,
    subDocs: [subSchema]
})

Then I would like to do:

exports.updateMyDocument = function(req, res) {
    var parentDoc = req.parentDoc; // The parent document. Set by parameter resolver.
    var document = req.myDoc; // Sub document of parent. Set by parameter resolver.
    var partialUpdate = req.body; // updated fields sent as json and parsed by body parser
    // I know that the statement below doesn't work, it's just an example of what I would like to do.
    // Updating only the fields supplied in "partialUpdate" on the document
    document.update(partialUpdate); 
    parentDoc.save(function(err) {
        if(err) {
            res.send(500);
            return;
        }
        res.send(204);
    }); 
};

Normally, I could achieve this using the $set operator, but my problem is that document in this example is a subdocument (embedded schema) of parentDoc. So when I tried to do

Parent.update({_id: parentDoc._id, "subDocs._id": document._id}, 
    {$set: {"subDocs.$" : partialUpdate}}, 
    function(err, numAffected) {});

it replaced the subdocument instance identified by subDocs._id. Currently I have "solved" it by setting only fields manually, but I was hoping for a better way to do this.

Answer 1

Build up a $set object programmatically based on the fields of partialUpdate to update just those fields using dot notation:

var set = {};
for (var field in partialUpdate) {
  set['subDocs.$.' + field] = partialUpdate[field];
}
Parent.update({_id: parentDoc._id, "subDocs._id": document._id}, 
    {$set: set}, 
    function(err, numAffected) {});