pull value from object -> array -> object -> object mongo

Question

I have this following strtucture

{
  _id: ".....",
  a: {
    a1:".......",
    b: [
      b1: {
        b11: "......",
        b12: "......",
      },
      b2: {
        b21: "......",
        b22: "......",
        d: {},
      },
      c:{
        c1: {
          ......
        },
        d: {

        }
      }
    ]
  }
}

here I want to check if property d exists or not inside b, it may exists in multiple objects inside b, if exists pull the d object from record.

Note: There might be a chance that property d exists multiple times inside b1 and b2, In this case I want to remove it from all objects

I tried like

Coll.find({ 'a.b': { $elemMatch: { 'c': { d: { $exists: true } } } } })

but it is not returning anything although there are record, any help appreciated.

I want to pull that data from record too.

Thanks.

UPDATE

Coll.find({ 'a.b.c.d'{ $exists: true } })

that worked for me but still no idea how to use positional operator to pull the value from record

Steve Tarver · Accepted Answer · 2015-10-25 04:49:24Z

1

Please take a little more time forming your questions to make them easier to answer: your example data has key-values inside a list (invalid), your question mentions $elemMatch which is a list operator, you talk about removing things but never follow up that thought, and then your UPDATE switches gears and implies it is an object hierarchy.

Taking a hint from your UPDATE, I created some valid data - paste this into mongo shell (perhaps in the test database):

db.test.insert({
  a: {
    a1: "a1",
    b: {
      b1: {
        b11: "b11",
        b12: "b12",
      },
      b2: {
        b21: "b21",
        b22: "b22",
        d: {},
      },
      c: {
        c1: {
          c1: "......"
        },
        d: {
          d1: "woo hoo, struck gold"
        }
      }
    }
  }
})

Inside the mongo shell, everything is javascript so "positional operators" are the dot and array subscript operator. A mongo find() returns an array of documents. If you want the the d document (object) from the first doc returned from the query

db.test.find({'a.b.c.d': {$exists: true}})[0].a.b.c.d

produces

{
  "d1": "woo hoo, struck gold"
}

UPDATE: Adding detail in response to comment.

If you want to remove the a.b.c.d sub-document, use $unset

// remove sub-document a.b.c.d
db.test.update({}, {$unset: {'a.b.c.d': ''}});
// look at the document to verify that a.b.c.d is removed
db.test.find();

edited Oct 25, 2015 at 4:49

answered Oct 24, 2015 at 21:40

Steve Tarver

3,2682 gold badges30 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Sasikanth Over a year ago

thanks for the answer, here b is array of objects, my record structure is correct I feel, . Coming to your answer I want to remove object d from record not to get the data, I can read the data, but to pull data from record I can't find exact query

Steve Tarver Over a year ago

On arrays: try to insert your example into a collection - review the error. On removing: use $unset to remove a single field. Updating my answer to show how.

Collectives™ on Stack Overflow

pull value from object -> array -> object -> object mongo

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related