DataTable.GetChanges() keeps returning NULL!

Question

I am trying to get all the rows that exist in allData but not in removeData

public static DataTable RemoveDuplicateRows(DataTable allData, 
    DataTable removeData) 
{
    removeData.Merge(allData);
    DataTable newData = removeData.GetChanges(); 
    removeData.RejectChanges();
    return newData;
}

removeData is empty prior to the call in this case (just a new DataTable();)

But newData always has a value of null after the DataTable newData = removeData.GetChanges(); line

Final Solution:

 public static DataTable RemoveDuplicateRows(DataTable allData, DataTable removeData) 
 {
  DataTable duplicate = allData.Clone();
  foreach (DataRow row in allData.Rows)
  {
   duplicate.ImportRow(row);
  }
  foreach (DataRow row in duplicate.Rows)
  {
   row.SetAdded();
  } 

  removeData.Merge(duplicate);
  DataTable newData = removeData.GetChanges(DataRowState.Added);
  removeData.RejectChanges();
  allData.RejectChanges();
  return newData;
 }

Answer 1

Your removeData DataTable needs to have the same columns/fields as allData. In other words, it can't just be a new DataTable().