Graeme Geldenhuys wrote: > On 1/15/07, Al Boldi <[EMAIL PROTECTED]> wrote: > > > 4. *Tight coupling to a data access API.* The BDE allows us to swap > > > aliases when you want to change databases, but what if you want to > > > switch from BDE data access, to ADO, IBObjects, Direct Oracle Access > > > (DOA), ClientDataSet or our own custom data format? (This is not the > > > fault of the data aware controls, but is still a problem with the > > > component-on-form style of developing.) > > > > What problem? Can you explain? > > Switching from the BDE to lets say Direct Oracle Access. You would > have to replace all you TDatabase, TQuery, TStoredProc components with > TDOADatabase, TDOAQuery and TDOAStoredProc components. You can't do > that with a search and replace and you can't do that at runtime. Also > if you listened to BDE specific exceptions, you would have to change > that code as well. All this is not a trivial change!
You could get the same kind of problem, when switching from tiOPF to InstantObjects. Think of BDE as Persistence layer, just like InstantObjects or tiOPF. When you change that layer, and your design does not easily support it, then you are in trouble no-matter what you use. > > Can you give an example of a simple generic implementation? > > To find out more about the Model-GUI-Mediators (MGM) pattern, have a look > at: http://www.atug.com/andypatterns/mgm.htm Thanks! The concepts discussed there pretty much nail the problem. While the mediator/adapter allows loose coupling of disparate objects, you still need specific mediators for each model-to-gui pair. No generalization is possible. The only, yet important, aspect you gain, is de-coupling. > For my implementation which rather uses RTTI to set and get Object > property values have a look at: > http://tinyurl.com/y5akb5 > > and the following units. > tiGenericEditMediators.pas > tiGenericListMediators.pas > tiCompositeMediators.pas > > My implementation is more complicate that it needs to be, just because > I wanted to implement a Generic Mediator class I can use for any Edit > components (TEdit, TTrackBar, etc). If can be simplified a lot! Also > my mediators use TtiObject as the base object for the Model, but that > is because I use tiOPF. Thanks again. I like it. You try to achieve genericity by making the mediator multi-widget aware. > It is very easy to change to any TObject > descendant class that as RTTI enabled and a simple implementation of > the Observer pattern. MGM is a compound pattern based on the Observer > and Mediator pattern. I would love to see a truly generalized implementation that would allow a single mediator adapt disparate objects. Is this possible? Thanks! -- Al _________________________________________________________________ To unsubscribe: mail [EMAIL PROTECTED] with "unsubscribe" as the Subject archives at http://www.lazarus.freepascal.org/mailarchives
