How to set the value in the drop down list.

Hi,

   I have 2 tables Employee and Works_On.While assigning work to employee i selected employee name in the drop down list.While storing those details in the works_on table i should store emp_id in the place of employee name.

  In c# for drop down list i used sqldatasource and selected emp_name field from employee table.How to return emp_id.Do i need to implement it in the coding or in the properties?