Explicit locking of Entity JavaBean

Question

Hi!
I am developing local WD application based on EJB model using SAP NetWeaver Developer Studio 7.0.12
There's Employee entity javabean, that is shown as a table on EmployeeView webdynpro view (model node, bound to controller).
There's also EmployeeEdit webdynpro view, where Employee entity javabean is shown as set of InputFields (same model node, bound to controller).
When user clicks Save button in EmployeeEdit view, changed values are saved.
The problem arises when two users want to change the same record of Employee entity. Both can go to EmployeeEdit view, change values of record and click Save button, because actual transaction for saving is implemented only when users click Save button.
The workaround for this would be explicit locking of entity record when first user goes to EmployeeEdit view, if it's not already locked. But I couldn't find enough information about this.
[EJBLocking interface|http://help.sap.com/javadocs/nw04/current/en/com/sap/engine/interfaces/ejb/locking/EJBLocking.html] might be what I need, but I don't know how to use it.
Can anyone give me an idea about all this?
Thanks in advance
Renat

Answer 1

Hi, Ganga!
Thank You for reply,
I've already chosen "Local" locking for my entity bean and trying to realize explicit locking for my entity.
I can't understand, what parameters do I need to pass to lock method.
Here is code of entity home method, which is called to lock this entity.
     public void ejbHomeLockMe() {
          EJBLocking ejbl = null;
          Context ctx = null;
          try {
               ctx = new InitialContext();
               ejbl = (EJBLocking) ctx.lookup("java:comp/EJBLocking");
          } catch (NamingException ne) {
               ne.printStackTrace();
               throw new OklaException(ne.getMessage());
          try {
               DataSource ds = (DataSource) ctx.lookup("jdbc/OKLA_DS");
               ejbl.lock( //here I get NullPointerException
                    TableLocking.LIFETIME_TRANSACTION,
                    ds.getConnection(),
                    (EntityBean) this,
                    TableLocking.MODE_EXCLUSIVE_NONCUMULATIVE);
          } catch (SQLException sqle) {
               sqle.printStackTrace();
               throw new OklaException(sqle.getMessage());
          } catch (NamingException ne) {
               ne.printStackTrace();
               throw new OklaException(ne.getMessage());
As a result I get this exception
   java.lang.NullPointerException
    at com.sap.engine.services.ejb.entity.pm.lock.EJBLockingImpl.getPKMap(EJBLockingImpl.java:108)
    at com.sap.engine.services.ejb.entity.pm.lock.EJBLockingImpl.lock(EJBLockingImpl.java:48)
    at my.company.okla.employee.EmployeeBean.ejbHomeLockMe(EmployeeBean.java:92)
Any thoughts about this?
Many thanks
Renat