Patterns for the overlap of two objects

Question

I'm sure this has already been asked and answered so I apologize in advance for that but I'm not figuring out the correct keywords to search for. Searching for "Pattern" hits way too many Q & A's to be useful.

I'm working on a regression testing app. I'm displaying a form on the screen and according to which user is logged in to the app some of the fields should be read-only. So I can abstract a field object and I can abstract a user object but what pattern should I be looking at to describe the intersection of these two concepts? In other words how should I describe that for Field 1 and User A, the field should be read-only? It seems like read-only (or not) should be a property of the Field class but as I said, it depends on which user is looking at the form. I've considered a simple two-dimensional array (e. g. ReadOnly[Field,User] = True) but I want to make sure I've picked the most effective structure to represent this.

Are there any software design patterns regarding this kind of data structure? Am I overcomplicating things--would a two-dimensional array be the best way to go here? As I said if this has been asked and answered, I do apologize. I did search here and didn't find anything and a Google search failed to turn up anything either.

Answer 1

At first blush it sounds more like you have two different types of users and they have different access levels. This could be solved by inheritance (PowerUser, User) or by containing a security object or token that sets the level for the user.

If you don't like inheritance as a rule, you could use a State pattern on the application, Decorate the user objects (Shudder) or possibly add strategy patterns for differing security levels. But I think it's a little early yet, I don't normally apply patterns until I have a firm idea of how the item will grown and be maintained.

Answer 2

Table driven designs can be effective. Steve Maguire had few nice examples in Writing Solid Code .

They are also a great way to capture tests, see fit .

In your case something like:

Field1ReadonlyRules = {
    'user class 1' : True,
    'user class 2' : False
}

field1.readOnly = Field1ReadonlyRules[ someUser.userClass ]

As an aside you probably want to model both users and user classes/roles/groups instead of combining them. A user typically captures who (authentication) while groups/roles capture what (permissions, capabilities)