How to return nested document with Mongoose?

Question

If I have this collection

[
  {
    "_id": "637cbf94b4741277c3b53c6c",
    "text": "outter",
    "username": "test1",
    "address": [
      {
        "text": "inner",
        "username": "test2",
        "_id": "637cbf94b4741277c3b53c6e"
      }
    ],
    "__v": 0
  }
]

and would like to search for the nested document by _id and return all of the nested document. If I do

db.collection.find({
  _id: "637cbf94b4741277c3b53c6c"
},
{
  address: {
    $eq: {
      _id: "637cbf94b4741277c3b53c6e"
    }
  }
})

I get

query failed: (Location16020) Expression $eq takes exactly 2 arguments. 1 were passed in.

Playground link

Question

Can anyone see what I am doing wrong?

Mohamed Oraby · Accepted Answer · 2022-11-22 13:50:15Z

1

use $elemMatch and also you have extra unneeded brackets. try

db.collection.find({
  _id: "637cbf94b4741277c3b53c6c",
  address: {
    $elemMatch: {
      _id: "637cbf94b4741277c3b53c6e"
    }
  }
})

Edit: if you only want to return the address add projection like this

db.collection.find({
  _id: "637cbf94b4741277c3b53c6c",
  address: {
    $elemMatch: {
      _id: "637cbf94b4741277c3b53c6e"
    }
  }
},
{
  _id: 0,
  address: 1
})

edited Nov 22, 2022 at 13:50

answered Nov 22, 2022 at 13:47

Mohamed Oraby

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5 Comments

Sandra Schlichting Over a year ago

It also returns the parent, which I an not interested in.

Mohamed Oraby Over a year ago

@SandraSchlichting edited the answer to only select address

Mohamed Oraby Over a year ago

@SandraSchlichting and by the way are you using find on purpose? are there gonna be multiple documents with certain specifications? if not you could use findOne which returns a single document

Sandra Schlichting Over a year ago

Ahh yes, I should use findOne(). Your code works perfectly. Is it possible to only return the value, and not the address key also? Like this?: pastebin.com/C6xxBwLw

nimrod serok Over a year ago

This solution will not work well if the array has more than 1 item...

nimrod serok · Accepted Answer · 2022-11-22 14:10:43Z

1

One option is to use find:

db.collection.find({},
{
  _id: 0,
  address: {
    $elemMatch: {
      _id: "637cbf94b4741277c3b53c6e"
    }
  }
})

See how it works on the playground example

The other option is to use aggregation pipeline:

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $in: [
          "637cbf94b4741277c3b53c62",
          "$address._id"
        ]
      }
    }
  },
  {
    $replaceRoot: {
      newRoot: {
        $first: {
          $filter: {
            input: "$address",
            cond: {
              $eq: [
                "$$this._id",
                "637cbf94b4741277c3b53c6e"
              ]
            }
          }
        }
      }
    }
  }
])

See how it works on the playground example

edited Nov 22, 2022 at 14:10

answered Nov 22, 2022 at 13:54

nimrod serok

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