Re: What databases have taught me
Date: Tue, 27 Jun 2006 22:48:42 -0700
Message-ID: <2006062722484275249-unclebob_at_objectmentorcom>
On 2006-06-23 11:29:40 -0700, frebe73_at_gmail.com said:
> In a recent thread Robert Martin suggested a similar class hierachy:
> Employee
> - Salaried employee
> - Hourly employee
> - Commissioned employee
>
> The Employee interface should have a calculatePayment method and the
> subclasses should have different implementations.
>
> This might look like a natural thing to do and it probably is while the
> problem solution is small and not very complex. But imagine that
> depending on what union branch the employee belongs too, the salary is
> calculated differently in some aspectes. Now you have to repeat this
> logic in all three implementations of calculatePayment. This is one
> example of problem you will encounter when you start with on dimension
> and later have to handle multiple dimensions.
You use the Bridge pattern.
|PaymentMethod|<-------|Employee|------>|UnionMembership|
A A
| |
+------+------+ +---------+--------+
| | | |
|HourlyMethod| |SalariedMethod| |NonMember| |Local705Member|
So, in fact, you don't have to repeat the implementation. Instead you create a different hierarchy that represents the union branch and pass the calculated pay to it.
To see this in action in much more detail I refer you to the Payroll solution in my book "Agile Software Development: Principles, Patterns, and Practices"
-- Robert C. Martin (Uncle Bob) | email: unclebob_at_objectmentor.com Object Mentor Inc. | blog: www.butunclebob.com The Agile Transition Experts | web: www.objectmentor.com 800-338-6716 |Received on Wed Jun 28 2006 - 07:48:42 CEST