String Literal Issue in findOneAndUpdate Mongoose Function

Question

Similar to this issue https://stackoverflow.com/questions/11183480/how-to-set-key-by-var-in-mongoose-node-js# = I cannot get the field variable in the findOneAndUpdate function. It takes it as literal field. I tried to implement their solution but it did not work. I didn't get an error it just didn't update anything.

var cat = new Cat();

var field = (req.body[1].type);

Cat.findOneAndUpdate({ 'sid': req.sessionID }, {$push: {field: req.body[0]}}, {'upsert': true, 'new': true}, function (err, data){

Answer 1

You need to use the bracket [] notation in order to set the "key" of an object property to a value from a variable:

var cat = new Cat();

// Just use it in the below assignment instead
//var field = (req.body[1].type);

var update = { "$push": { } };
update.$push[req.body[1].type] = req.body[0];

Cat.findOneAndUpdate(
    { 'sid': req.sessionID },
    update,                      // and reference in here
    {'upsert': true, 'new': true}, 
    function (err, data){

That's how to dynamically assign a key in JavaScript.