variable with mongodb dotnotation

Question

I want to increase a field inside an object object inside a mongodb document by 1.

  var stuffID = 5
  collection.update({
    \"id\": id,
  },
  {
    \'$in         


        

Answer 1

Put the variable where it says stuffID.

'stuff.' + varname: 1

Answer 2

You need to create your variably-keyed object separately, because JS before ES2015 doesn't permit anything other than constant strings in object literal syntax:

var stuffID = 5
var stuff = {};                 // create an empty object
stuff['stuff.' + stuffID] = 1;  // and then populate the variable key

collection.update({
    "id": id,
}, {
    "$inc": stuff               // pass the object from above here
}, ...);

EDIT in ES2015, it's now possible to use an expression as a key in an object literal, using [expr]: value syntax, and in this case also using ES2015 backtick string interpolation:

var stuffID = 5;
collection.update({
    "id": id,
}, {
    "$inc": {
        [`stuff.${stuffID}`]: 1
    }
}, ...);

The code above works in Node.js v4+