You are trying to create a way for an employee to enroll in a training course right?
You're probably better off replacing the nested data view with a data grid showing all the training courses the employee is enrolled in. An entity 'enrollments' if you will.
You can then add new enrollments for the employee by a new/edit form where you a.) select a training course provider b.) select a course (constrained on a) c.) select a date (constrained on b)