MongoDB - How to rename the specific field from list of unstructured array field?

Question

I have several documents as given below. Now I need to do rename the middlename field into mid_name if middlename exists in the document.

{
    "id":"abc",
    "name":[
      {
          "first_name":"abc",
          "last_name":"def"
      },
      {
          "first_name":"ghi",
          "last_name":"mno",
          "middilename":"xyz"
      }
    ]
}

This is something that I expect it to be.

{
    "id":"abc",
    "name":[
      {
          "first_name":"abc",
          "last_name":"def"
      },
      {
          "first_name":"ghi",
          "last_name":"mno",
          "mid_name":"xyz"
      }
    ]
}

And this is what I have done but it throws the error.

db.md_carrierInformation.updateMany({"name.middlename":{$exists:true}}, {$rename:{"name.$.middlename":"name.mid_name"}})

ERROR

MongoServerError: The source field for $rename may not be dynamic: name.$.middlename

Answer 1

Work on the update with the aggregation pipeline.

1. $set - Set name array field.

   1.1. $map - Iterate each item in name array and return new array.

   1.2. $cond - Condition for checking current document's middlename is not existed.

   1.2.1. If true, with merge current document with the document with field mid_name via $mergeObjects.

   1.2.2. If false, remain the existing document.

2. $unset - Remove field for name.middlename.

db.md_carrierInformation.updateMany({
  "name.middlename": {
    $exists: true
  }
},
[
  {
    $set: {
      "name": {
        $map: {
          input: "$name",
          in: {
            $cond: {
              if: {
                $ne: [
                  "$$this.middlename",
                  undefined
                ]
              },
              then: {
                $mergeObjects: [
                  "$$this",
                  {
                    mid_name: "$$this.middlename"
                  }
                ]
              },
              else: "$$this"
            }
          }
        }
      }
    }
  },
  {
    $unset: "name.middlename"
  }
])

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