A use-case implementation question

[Behrang Saeedzadeh <be...@gmail.com>]

Hi,

Suppose that I have a use case in which I have to develop a UI with JSF, and
without Seam or Shale, for the following task:

	We have a bunch of roles and positions. Each position may have one or more
	roles. Design a UI for assigning roles to a selected position. Use a
	selectManyListBox for selecting the roles to be assigned to the user.
	The roles and positions are stored in a backend database and their count
	might change over time.
	
Ideally, I would use a request-soped bean with such an interface to implement
my case:

	public interface IRoleAssignmentBean {
		
		setSelectedPosition(Position aPosition);
		Position getSelectedPosition();
		
		List<Role> getCurrentAssignedRoles(); // fetches from DB
		List<SelectItem> getAllRoleItems(); // fetches from DB
		
		void assignedRolesChanged(ValueChangeEvent vce); // updates the DB
		
	}
	
The getCurrentAssignedRoles and getAllRoleItems fetch the items from database.
getCurrentAssignedRoles, for example, has an implementation like this;

	List<Role> getCurrentAssignedRoles() {
		
		if (getSelectedPosition == null) {
			throw new RuntimeException("blah blah");
		}
		
		if (currentAssignedRoles == null) {
			currentAssignedRoles =
roleDao.findCurrentAssignedRoles(getSelectedPosition());
		}
		
		return currentAssignedRoles;
	}
	
(Question: how would you implement this getter?)
	
Then in my JSF page, I would like to have:

	<h:selectOneCheckBox value="#{RoleAssignmentBean.currentAssignedRoles}"
		valueChangeListener="#{RoleAssignmentBean.assignedRolesChanged}">
		<f:selectItems value="#{RoleAssignmentBean.allRoleItems}" />
	</h:selectOneCheckBox>
	
But this ain't gonna work as I don't have the setCurrentAssignedRoles method.
I can add the setter to my bean, but then this makes the currentAssignedRoles
property ambiguos: sometimes it contains the roles that are currently stored
in the database, sometimes it contains the roles submitted by the user.

I could use a custom component like this:

	<custom:selectOneCheckBox
		value="#{RoleAssignmentBean.currentAssignedRoles}"
		submittedValue="#{RoleAssignmentBean.submittedAssignedRoles}"
		valueChangeListener="#{RoleAssignmentBean.assignedRolesChanged}">
		<f:selectItems value="#{RoleAssignmentBean.allRoleItems}" />
	</custom:selectOneCheckBox>
	
And add another property, namely submittedAssignedRoles, to
disanbiguate the case.

But I think that there should be something that I don't know. I mean this is a
very common use case and it should be possible to implement it by using the
standard components, and at the same time with a clean and well-designed
backing bean.

If my approach is not correct, could someone give me some advice on
what the correct approach would be?

Regards,
Behi

-- 
"Science is a differential equation. Religion is a boundary condition"
- Alan Turing

Behrang Saeedzadeh
http://www.jroller.com/page/behrangsa
http://my.opera.com/behrangsa