Convert simple array into nested array

I am trying to convert a simple array into an array of arrays while retaining the existing values:

roles: Array

into this:

roles: Array
  [name: "mentor",
   startDate: "01-01-1900",
   endDate: "12-31-2099"],
  [name: "engineer",
   startDate: "01-01-1900",
   endDate: "12-31-2099"] 

Everything I have tried wipes out my existing values.


Hello @Austin_Summers,

Your question is not clear to me, what are you trying to do:

  1. Do you want to update the existing document’s field?
  2. Do you want to format the result by a find/aggregation query?
  3. Where are these startDate and endDate coming from? Is it external input or internal fields?
  4. FYI: Your expected result array is not a valid array/object.

It will help us if you post an example document, and whatever query that you tried.

Hello @turivishal,

I am looking to reformat the existing data structure without losing the existing data.
This will be part of a larger set of updates to change and add other fields.
The fields will eventually be updated by a tool in current development.

I tried a $map that added the date fields, but wiped out the existing data.

   { name: "Jon Doe" },
    $set: {
      roles: {
        $map: {
          input: "$roles",
          in: {
            name: "$$",
            startDate: null,
            endDate: null

here you need to just use "$$this" instead of "$$" because roles existing value has an array of strings.

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Thank you!
I just tried that myself. I am still very fuzzy on the use of $$this within aggregations.

Thanks again.

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Look at the documentation of $map aggregation array operator,

It is explained everything perfectly with the example.

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