Gilles Ganault wrote: > >> We haven't used TDataSource in quite some time and actually don't miss it. >> > > I didn't know you could do away with all those components to connect > DB-aware widgets. If you have some DelphiWin32 "hello, world" sort of > code, I'm very interested :-) >
You can't. You lose the db aware aspect, but what I'm saying is it isn't as "bad" as I used to think. > >> Although for years I was concerned about the cost in programmer time of >> using disconnected components, I've found the gains from using >> TDataSource are outweighed by the non-deterministic behavior of the data >> connections. >> > > Care to be more specific? In short, what are the drawbacks about using > Table/Query + DataSource? > The primary source of non-determinism is that the user tends to get involved. Most code is triggered by events, which works up to a point. Once the model breaks down, it does so in a way which cannot be easily worked around. I can recall many times having to stick convoluted logic to handle the case of one field being updated which causes other data to be affected. By going to a non data-aware model, all those issues disappear because your posting logic becomes 100% deterministic. There are no side effects due to events firing off. As a generic example, if you attach something like a grid to a table, you must either maintain an open connection to the table or transfer the data into a memory table. Keeping a live connection is potentially dangerous and memory consumptive. Using a memory table is useful in small circumstances, but once you reach a certain amount of rows, you end up writing caching code to maintain performance. For this example, the solution I've found which works is to have a non-data aware grid in virtual mode. The system uses a data supply model which figures out what is to be displayed and supplies it to the grid on demand. It's scary at first, because you feel like you are re-inventing the wheel, but you quickly find out you are not. TDataSource/TDataLink was a good idea in its time, but it is way out of date and, in my experience, creates as many problems as it solves once you start building more complex user-centric GUIs. FWIW John Elrick Fenestra Technologies _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
