MongoDB: How do I find number of items in embedded document?

Question

My schema looks like

name:
value:
p_vars: {
    name1: {},
    name2: {},
}

I want to count how many items are there in p_vars.

Thinking that interpretor is JavaScript, I tried

db.collection.findOne().p_vars.length

But nothing returns

Answer should be

Considering above, answer should be 2(two items name1 and name2)

`p_vars` is an object. Objects don't have lengths in javascript. Why exactly did you expect this to work? — Sergio Tulentsev, Jul 20 '12 at 22:13
I want to know how many items are in p_vars, like count of `name1` + `name2` + .... — daydreamer, Jul 20 '12 at 22:14
As this is a javascript object, maybe this question helps: http://stackoverflow.com/questions/956719/number-of-elements-in-a-javascript-object — Eduardo, Jul 20 '12 at 22:16

Adam Comerford · Answer 1 · 2015-04-13T14:24:57.183

The simplest solution here is to change your schema to use an array of p_vars, which it sounds like you want anyway. If instead the schema was:

name:
value:
p_vars: [
    name1: {},
    name2: {},
]

Then the db.collection.findOne().p_vars.length command would return 2 as you expect.

With the original schema, the only option I think you have is to write a JS function to iterate and count the elements manually.

1 Answers1