What happens when you apply RejectChanges method on a DataSet?

Answer:

Let's consider, a DataSet contains 3 tables. When you will apply RejectChanges() method, it will be automatically invoked on all the 3 tables in the dataset. So any changes that were done with the tables will be rolled back.

When you call DataTable.RejectChanges method, the rows that are in edit-mode will cancel their edit. It will remove the new added rows. It will also return back all modified and deleted rows to its original state.