I have a problem in my project in duplication
I have students that will register in many courses but when I for example register for student John in JAVA course and come again and register John in the same subject JAVA it will registered successfuly (endless registeration in the same class) So I need just one time without duplication.
plz help me by any thing.
I have heared about annotation for that so plz help me to avoid such problem.
