Azure Data Factory Copy Data activity - Use variables/expressions in mapping to dynamically select correct incoming column - azure-data-factory

Question

I have the below mappings for a Copy activity in ADF:
"translator": {
"type": "TabularTranslator",
"mappings": [
{
"source": {
"path": "$['id']"
},
"sink": {
"name": "TicketID"
}
},
{
"source": {
"path": "$['summary']"
},
"sink": {
"name": "TicketSummary"
}
},
{
"source": {
"path": "$['status']['name']"
},
"sink": {
"name": "TicketStatus"
}
},
{
"source": {
"path": "$['company']['identifier']"
},
"sink": {
"name": "CustomerAccountNumber"
}
},
{
"source": {
"path": "$['company']['name']"
},
"sink": {
"name": "CustomerName"
}
},
{
"source": {
"path": "$['customFields'][74]['value']"
},
"sink": {
"name": "Landlord"
}
},
{
"source": {
"path": "$['customFields'][75]['value']"
},
"sink": {
"name": "Building"
}
}
],
"collectionReference": "",
"mapComplexValuesToString": false
}
The challenge I need to overcome is that the array indexes of the custom fields of the last two sources might change. So I've created an Azure Function which calculates the correct array index. However I can't work out how to use the Azure Function output value in the source path string - I have tried to refer to it using an expression like #activity('Get Building Field Index').output but as it's expecting a JSON path, this doesn't work and produces an error:
JSON path $['customFields'][#activity('Get Building Field Index').outputS]['value'] is invalid.
Is there a different way to achieve what I am trying to do?
Thanks in advance

Answer 1

I have a slightly similar scenario that you might be able to work with.
First, I have a JSON file that is emitted that I then access with Synapse/ADF with Lookup.
I next have a For each activity that runs a copy data activity.
The for each activity receives my Lookup and makes my JSON usable, by setting the following in the For each's Settings like so:
#activity('Lookup').output.firstRow.childItems
My JSON roughly looks as follows:
{"childItems": [
{"subpath": "path/to/folder",
"filename": "filename.parquet",
"subfolder": "subfolder",
"outfolder": "subfolder",
"origin": "A"}]}
So this means in my copy data activity within the for each activity, I can access the parameters of my JSON like so:
#item()['subpath']
#item()['filename']
#item()['folder']
.. etc
Edit:
Adding some screen caps of the parameterization:
https://i.stack.imgur.com/aHpWk.png