Update all nested array records if a field does not exist in mongodb

Question

I have the object below. "questions" is the document name and each question has a nested array of type answers property where some answers has a propoerty call status.

questions = [
{
    "_id": "idq1"
    "author" :"auth1"
    "Answers": []
},
{
    "_id": "idq2"
    "author" :"auth2"
    "Answers": [
        {
            "author": "auth1",
            "comments" [...],
            "status" : "1"
        },
        {
            "author": "auth2",
            "comments" [...],
        },
        {
            "author": "auth3",
            "comments" [...],
            "status" : "0"
        }
    ]
}
]

I need to update all the nested Answers.status = "1" , where the Answers length > 0 and the nested element "status" does not exist. so the result would be :

questions = [
{
    "_id": "idq1"
    "author" :"auth1"
    "Answers": []
},
{
    "_id": "idq2"
    "author" :"auth2"
    "Answers": [
        {
            "author": "auth1",
            "comments" [...],
            "status" : "1"
        },
        {
            "author": "auth2",
            "comments" [...],
                "status" : "1"
        },
        {
            "author": "auth3",
            "comments" [...],
            "status" : "0"
        }
    ]
}
]

Is "questions" also a field? Can you add the proper sample document? — Vijay Rajpurohit
– Vijay Rajpurohit, Commented May 26, 2020 at 4:27
questions is the document name and each question has a nested answers property where each answers has a status. — Hosein Djadidi
– Hosein Djadidi, Commented May 26, 2020 at 4:32

Vijay Rajpurohit · Accepted Answer · 2020-05-26 04:54:12Z

You can use the arrayFilters for updating the array fields

Here I'm adding the query to update the document as required:

I have used the multi: true along with the arrayFilter to update multiple documents.

db.questions.update(
  {
    "Answers":{
      $nin:[
        [],
        null
      ]
    }
  },
  {
    $set:{
      "Answers.$[ans].status":"1"
    }
  },
  {
    arrayFilters:[
      {
        "ans.status":{
          $exists:false
        }
      }
    ],
    multi:true
  }
)

Sample output

{
    "_id": "idq1"
    "author" :"auth1"
    "Answers": []
},
{
    "_id": "idq2"
    "author" :"auth2"
    "Answers": [
        {
            "author": "auth1",
            "comments": [...],
            "status" : "1"
        },
        {
            "author": "auth2",
            "comments": [...],
            "status" : "1"
        },
        {
            "author": "auth3",
            "comments": [...],
            "status" : "0"
        }
    ]
}

For more about arrayFilters refer here.

Hope this will help :)

Instead of $nin. best to use { "Answers.1" : {$exists : true} }

Hosein Djadidi · Accepted Answer · 2020-05-26 05:17:47Z

1

My latest working code :

questions.updateMany(
            {
                "Answers.status" :null
            },
            { $set: { "Answers.$[i].status": 1 } },
            { new: true,
                arrayFilters: [{ "i.status": null}]        
            });

answered May 26, 2020 at 5:17

Hosein Djadidi

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1 Comment

Vijay Rajpurohit Over a year ago

But this will not be able to update the "status" field if the "status" is not present in two or more documents of the same "Answers" array. If that's not the use case then it's okay :)

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