ABAP_to_the_Future

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Web Dynpro ABAP and Floorplan Manager
is to change the model (although the latte r is not impossible either). Therefore,
putting the model inside the view is no t the way forward; the model should go
nowhere near this area. (Strangely, ithas been said that “SAP forbids SELECT statements
within views,” but this is not enforced by the syntax check—you don’t get
a warning and it all works fine. So by “forbid,” it would seem that SAP presumes
that you won’t do it if you’re told not to.)
Another recommendation is to not put any references to the model class (or any
SELECT statements) in the view. Even if it is technically possible to do so, it paints
you into a corner. You will see later on in this chapter how you use the code in
the view to delegate tasks upwards (which, as an aside, is exactly what you do in
classical DYNPRO modules as well).
Model as an Assistance Class
Using the model as an assistance class isanother option. A WDA application looks
somewhat like a tree structure, and right at the top you can declare an assistance
class. This class then pops up automatically as a member variable of all the controllers
within the application.
At first glance, this looks like the idea l place to put your model class, and some
articles about WDA suggest just this approach. However, housing a model class
does not seem to be what an assistance class was intended to do; its purpose
seemed to be very WDA-specific and to revolve around handling texts (such as
field labels) throughout the application. If you’re a pu rist, you’d also be uncomfortable
with one class doing two dispar ate things; this would mean that you
would have to make your model inherit from a WDA-specific abstract class. Your
model class would then be tightly coupled to the WDA framework (the opposite
of what you generally want to achieve) as well as doing two different things:
model-type things and WDA-specific text things.
It is also possible to use the assistance class as a go-between linking the real model
to the WDA application. In this scenario, the assistance class would still be doing
two things, but you could reuse existing models and they would not be tied to the
WDA framework. However, if you take this approach, then the views can call the
model methods directly, and you are back to the problem with the model and the
view tied together, so it is difficult to change one without the other. It seems that
all those OO books (see the end of the chapter for some recommendations) actually
put in all these rules about separation of concerns for a very good reason. As
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