using $exists in Mongo with dynamic key names and the native driver for node

Question

using $exists in Mongo with dynamic key names and the native driver for node

I have a document in a collection like so:

{
  container : {
    P39433: 2,
    P30213: 4
  }
}

The values 'P39433' and 'P30213' are dynamically generated in the program. I can run the following query using the dot notation against mongo directly and I get the desired result

db.collection.findOne({ "container.P00000" : { $exists : false } })

I get the document back. i.e. I only want to get the document if the field does not exist.

My question is how can I run that query in Node using the native driver when the value P00000 is contained in a variable.

My usual solution is to structure the query like below but it does not return a result.

var fieldName = 'P00000';
var dynObj = {};
dynObj[fieldName] = { $exists : false };
db.collection.findOne( { "container" : dynObj });

node.js
mongodb

Answer 1

You're close. Try this:

var fieldName = 'P00000';
var dynObj = {};
dynObj["container." + fieldName] = { $exists : false };
db.collection.findOne(dynObj);