How to find an object which is at nth nested level in mongoDB? (single collection, single document)

Question

I am trying to find an nth object using '_id', which is in the same document.

Any suggestions or references or code samples would be appreciated.

(e.g)

Document will look as below:

{
    "_id": "xxxxx",
    "name": "One",
    "pocket": [{
        "_id": "xxx123",
        "name": "NestedOne",
        "pocket": []
    }, {
        "_id": "xxx1234",
        "name": "NestedTwo",
        "pocket": [{
            "_id": "xxx123456",
            "name": "NestedTwoNested",
            "pocket": [{"_id": "xxx123666",
                "name": "NestedNestedOne",
                "pocket": []
            }]
        }]
    }]
}

The pockets shall hold more pockets and it is dynamic.

Here, I would like to search "pocket" using "_id" , say "xxx123456", but without using static reference.

Thanks again.

Is difficult to updated nested dynamic keys and is not good practice to keep data in too nested. After looking your documents I don't understand why you put `pocket inside pocket inside pocket...` is better way to changed documents structure and then used update — Neo-coder, May 26 '15 at 12:50

score 0 · Answer 1 · edited May 23 '17 at 12:30

I highly recommend you change your document structure to something easier to manage/search, as this will only become more of a pain to work with.

Why not use multiple collections, like explained in this answer?

So an easy way to think about this for your situation, which I hope is easier for you to reason about than dropping some schema code...

Store all of your things as children in the same document. Give them unique _ids.
Store all of the contents of their pockets as collections. The collections simply hold all the ids that would normally be inside the pocket (instead of referencing the pockets themselves).

That way, a lot of your work can happen outside of DB calls. You just batch pull out the items you need when you need them, instead of searching nested documents!

However, if you can work with the entire document:
Looks like you want to do a recursive search a certain of number of levels deep. I'll give you a general idea with some pseudocode, in hopes that you'll be able to figure the rest out.

Say your function will be:

function SearchNDeep(obj, n, id){
  /**
  You want to go down 1 level, to pocket
  see if pocket has any things in it. If so:
  Check all of the things...for further pockets...

  Once you've checked one level of things, increment the counter.
  When the counter reaches the right level, you'd want to then see if the object you're checking has a `'_id'` of `id`.
**/
}

That's the general idea. There is a cleaner, recursive way to do this where you call SearchNDeep while passing a number for how deep you are, base case being no more levels to go, or the object is found.

Remember to return false or undefined if you don't find it, and the right object if you do! Good luck!

How to find an object which is at nth nested level in mongoDB? (single collection, single document)

1 Answers1