Unable to reference another dataset column in other schema

#1

I have a dataset of following JSON structure.

[{
		"articles": [{
			"action": "edit",
			"messageId": "75ab4788-af4e-478d-bb84-b5d5d5c4c080",
			"articleNumber": "3313"

		}]
	},
	{
		"articles": [{
			"action": "add",
			"messageId": "15ab4788-af4e-478d-bb84-b5d5d5c4c090",
			"articleNumber": "5316"

		}]
	}
]

I want to reference “articleNumber” property in another schema, but getting error which is below.

[{
  "purchaseOrders": [
    {
      "action": "delete",
      "lines": [
        {
          "articleNumber": "error: no implicit conversion of String into Integer"
        }
      ]
    }
  ]
}]

setup

Screenshot 2022-10-22 at 6.44.12 AM
Screenshot 2022-10-22 at 6.44.12 AM2850×610 81.4 KB

Can someone please suggest, If I am missing something.

#2

Try adding a formula looking like this:
this.to_i

or

this.to_s

The first will convert to an integer, the second will convert to a string.

#3

Not Working, this.to_i showing 0 all the time and this.to_s showing same implicit conversion error.