Update an object in a nested array with $set and $[identifier] (mongoDB 3.6)

Question

MongoDB 3.6 allow to perform complex array manipulations against all matching elements in any array – no matter how deeply nested – Update Nested Arrays with $[identifier]

Consider the document below on survey collection:

{
    "_id": "5a7d86d8fac139e71b0b9f5b",
    "results": [
      {
        "items": [
          {
            "comments": [
              {
                "id" : "123456",
                "email": "[email protected]",
                "content": "comment 1",
                "createdAt": "2018-05-03"
                "replies": []
              }
            ]
          }
        ]
      }
    ]
  }

I'm trying to update the comment email, content and createdAt fields and without touching to the id and replies fields.

I'm using $set and the new $[<identifier>]

I tried the command below based on The update command :

db.runCommand({
  update: "survey",
  updates: [
    {
      q: {},
      u: {
        $set: {
          "results.$[].items.$[].comments.$[comment]": {
            "email": "[email protected]",
            "content": "comment 2",
            "createdAt": "2018-05-04"
          }
        }
      },
      arrayFilters: [
        {
          "comment.id": { 
            $eq: "123456"
          }
        }
      ]
    }
  ]
})

The command works but it removes the id and replies fields.

Any help ? Thanks.

s7vr · Accepted Answer · 2018-02-09 17:47:51Z

4

$set with document {} overwrites the matching document. Use $set and list all the document fields using dot notation to perform field level updates. More here.

db.runCommand({
  update: "survey",
  updates: [
    {
      q: {},
      u: {
        $set: {
          "results.$[].items.$[].comments.$[comment].email": "[email protected]",
          "results.$[].items.$[].comments.$[comment].content": "comment 2",
          "results.$[].items.$[].comments.$[comment].createdAt": "2018-05-04"
        }
      },
      arrayFilters: [
        {
          "comment.id": { 
            $eq: "123456"
          }
        }
      ]
    }
  ]
})

answered Feb 9, 2018 at 17:47

s7vr

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2 Comments

Jawad Over a year ago

This is an alternative, but in case when we have a lot of fields to update, it will be difficult to list them all like this.

s7vr Over a year ago

Its either replace or you list them all. You can read all the fields from database and do a merge on client side and send the whole doc.

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