How to rename a field that is nested inside an array of objects deep without compromising on performance?

Working with Data
1

I wanted to rename field inside a nested array of objects which looks like below:

{
    "_id":"63ca455cb7dd228bcb3d85e5"
    "name": "Alex",
    "phoneNumber": "+235946546654",
    "level": 5,
    "workByCateg": [
      {
        "workId": "741qaz852wsx963edc",
        "customWork": [
          {
            "dName": "Status",
            "type": "options",
            "value": "Others"
          },
          {
            "dName": "Appointment",
            "type": "dateTime",
            "value": 1324645625
          },
          {
            "dName": "Notes",
            "type": "status",
            "value": "hi hello how are you.."
          }
        ]
      },
      {
        "workId": "123qaz456wsx789edc",
        "customWork": [
          {
            "dName": "Status",
            "type": "options",
            "value": "Work Done"
          },
          {
            "dName": "Appointment",
            "type": "dateTime",
            "value": 1326546546
          },
          {
            "dName": "Cus-Field",
            "type": "multi-options",
            "value": ["opt1", "opt2"]
          }
        ]
      }
    ]
  }

I want to retain this structure, but do some changes like the following, on the result:

  1. change the field name from “dName” to “name”
  2. remove the field “type” from “customWork” field.

I don’t want to make changes to the database.

The following is the aggregation that I use:

[
    {
      $match: <my_query>
    },
    {
      $unwind: "$workByCateg",
    },
    {
      $set: {
        workByCateg: {
          processId: "$workByCateg.workId",
          customWork: {
            $map: {
              input: "$workByCateg.customWork",
              as: "theField",
              in: {
                name: "$$theField.dName",
                value: "$$theField.value",
              },
            },
          },
        },
      },
    },
    {
      $addFields: {
        "workByCateg.customWork": {
          $ifNull: ["$customWork", "$$REMOVE"],
        },
      },
    },
    {
      $group: {
        _id: "$_id",
        name: { $last: "$name" },
        phoneNumber: { $last: "$phoneNumber" },
        level: { $last: "$level" },
        workByCateg: { $push: "$workByCateg" },
      },
    },
  ]

Here I’m doing unwind first, to change field names, and then im grouping it again to club all “customWork” together under “workByCateg” field.
I feel like the aggregation that i use is an overkill and thinking about performance issues. Any straight forward approach for this?

Any help would be appreciated. Thank you for your time.

2

Hi @Sooraj_S,
I believe we can take the following approach:

db.workers.updateMany(
  {},
  [
    {
      $set: {
        "workByCateg": {
          $map: {
            input: "$workByCateg",
            as: "work",
            in: {
              workId: "$$work.workId",
              customWork: {
                $map: {
                  input: "$$work.customWork",
                  as: "custom",
                  in: {
                    name: "$$custom.dName",
                    value: "$$custom.value"
                  }
                }
              }
            }
          }
        }
      }
    }
  ]
);

It would be good to test performance on a larger collection, and even adopt some kind of filter and run updateMany in batches.

See if it makes sense and let me know!

4

Hi, thanks for taking the time and replying.
I’m sorry that i didn’t mention that I don’t want to update the documents. I just want to modify it for the response.

This one updates the docs in the collection right? @Leandro_Domingues

5

Actually I believe I was the one who made a mistake, you really mentioned that you didn’t want to change the documents in the database, I’m sorry… Yes this script changes the documents in the collection.

Let me see if I can think of something.

6

Hi @Leandro_Domingues ,
Thanks, this one really helped.

Now, I’m really sorry for not testing out the aggregation method you mentioned.
I used your suggestion inside aggregation, rather than in updateMany, and it worked.

I request you to, if possible, edit your answer and update “updateMany” to “aggreate”, so that it helps others in need.
I’m marking your answer as the solution.

Thanks again. Cheers!

1 Like
7

Sure!

Here it goes, now without any changes to the database, using the aggregate to return the documents in the desired format.

db.workers.aggregate(
  [
    {
      $set: {
        "workByCateg": {
          $map: {
            input: "$workByCateg",
            as: "work",
            in: {
              workId: "$$work.workId",
              customWork: {
                $map: {
                  input: "$$work.customWork",
                  as: "custom",
                  in: {
                    name: "$$custom.dName",
                    value: "$$custom.value"
                  }
                }
              }
            }
          }
        }
      }
    }
  ]
);
1 Like
8

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