Oracle Forms

Hello All

I'm new to oracle forms, i'm using form's 6i...I'm designing a form to show the details of employees using the data block


Tables Used

Employee(EMp Details)
-------------
EMPLOYEE_ID (primary key)
EMPLOYEE_FIRST_NAME

Project(Project Details)
-------------
PROJECT_ID (primary key)
PROJECT_NAME

Employee_project(Emp Project Relations)
--------------------------
EMP_ID (foriegnkey)
PROJECT_ID (foriegnkey)

Ex:

EMP_id Project_id
101 301
101 302
102 303


I'm going to add and delete values from the Employee_project table only

I have run the form successfully with add,delete values

The problem is while adding new values during run time duplicate values is allowed

EX:

The Employee_project table contains already contains the values of

EMP_id Project_id
101 301
101 302
102 303

If i insert the same values during the form run time and press the "*SAVE*" button the same values are added to the table like

EMP_id Project_id
101 301
101 302
102 303
101 301
101 302
102 303

I want to prevent this duplicate entries

How to prevent the duplicate entry?

Is any trigger is used for this validatin?

Help me!