Using ADF Data Flow Derived Column transform against nested Delta structures - azure-data-factory-2

Question

I'm trying to use a derived column transform within an ADF (Gen 2) Data Flow where I've ingested a Delta table with nested structures. I'm struggling with the syntax needed to flatten out these structures and no column info is displayed despite me being able to preview the data.
Such a structure would be:
{
"ContactId":"1002657",
"Name":{
"FirstName":"Donna",
"FullName":"Donna Brittain",
"LastName":"Brittain"
}
}
Data Preview working OK:
Data Preview
The structure of my Delta table:
Delta Table Struct
The error I'm getting trying to reference a nested column:
Derived Column Task
How can I reference a nested column such as Name.FirstName to flatten it out to FirstName and why is it not showing up in any of the mappings?

Answer 1

There is a easy way to flatten the nested structures. We can use Copy activity in ADF firstly, it will automate flatten the nested column.
Copy the data into Azure Storage such as data lake(here I used Azure Data Lake Storage Gen 2), then we can use it as data source in the Data Flow.
We can create a txt or csv file with headers in data lake.
Then we can define a Copy activity in ADF and set the mapping.
After run debug, we can see the result. We can use it as data source in data flow.
Update:
In the sink,we can set the value of the Max rows per file option like follows:
ADF will divide the file into several files