[Lazarus] Propose: dont try to open TDBLookup* ListSource automatically

[Michael Van Canneyt]

On Sun, 8 Jul 2012, Luiz Americo Pereira Camara wrote:

> Currently the db lookup controls tries to open the dataset linked to 
> ListSource if is closed at lookup initialization.
>
> The initialization occurs after the control is loaded (streamed) or when a 
> related db property is changed in the control. This behavior can leads to 
> opening the dataset at unpredictable time or even twice (if the programmer 
> opens the dataset after loading of the control). Also it can trigger events 
> like AfterOpen in improper moments, e.g., data structures not initialized.
>
> Removing this feature, that is LCL specific, can have side effects in 
> projects that do not open explicitly the ListSource dataset or closes it when 
> the lookup control is still in use.
>
> Recently two bugs were reported due to this behavior (see 
> http://bugs.freepascal.org/view.php?id=22387 
> http://bugs.freepascal.org/view.php?id=22337 
> http://lazarus.freepascal.org/index.php/topic,17355.msg96112.html )
>
> So, removing this feature has the benefits of a cleaner code and better user 
> control when to open the dataset thus avoiding potential bugs and decreased 
> performance. The drawback is that it can affect programs that relies in that 
> behavior although it should be easily fixable and if there's a good moment 
> for such changes is now since 1.0 has already branched.
>

Why not introduce a boolean property OpenLookupDataset to control this behaviour ?

Michael.