How to get the Identity values in SQL BULK COPY?

Disclaimer: I'm the owner of the project Bulk Operations

In short, this project overcomes SqlBulkCopy limitations by adding MUST-HAVE features like outputting inserted identity value.

Under the hood, it uses SqlBulkCopy and a similar method as @Mr Moose answer.

var bulk = new BulkOperation(connection)

// Output Identity Value
bulk.ColumnMappings.Add("CustomerID", ColumnMappingDirectionType.Output);

// Map Column
bulk.ColumnMappings.Add("Code");
bulk.ColumnMappings.Add("Name");
bulk.ColumnMappings.Add("Email");

bulk.BulkInsert(dt);

EDIT: Answer comment

can I simply get a IList or simply , I see its saved back in the customers table, but there is no variable where I can get a hold of it, can you please help with that. So, I an insert in Orders.CustomerID table

It depends, you can keep a reference to the Customer DataRow named CustomerRef in the Order DataTable.

So once you merged your customer, you are able to populate easily a column CustomerID from the column CustomerRef in your Order DataTable.

Here is an example of what I'm trying to say: https://dotnetfiddle.net/Hw5rf3

Try this

CREATE TABLE #temp 
(
    DataRow varchar(max)
)
BULK INSERT #Temp FROM 'C:\tt.txt'  

ALTER TABLE #temp
ADD id INT IDENTITY(1,1) NOT NULL

SELECT * FROM #temp