Re: APQ

["Warren W. Gay VE3WWG" <ve3wwg@NoSpam.cogeco.ca>]

Brian May wrote:
> Hello,
> 
> Here are my suggested changes to APQ (not actually done or tested).

I'll just respond briefly here, since I am on my way to
work..

> 1. Decide on or write a "smart pointer" library. ie. a library that
> manages pointers based on a reference count. Obviously the license
> must be compatible with the license of APQ.
> 
> 2. No change to Connection_Type or Root_Connection_Type.
> 
> 3. Create new Database_Type. This type should not be
> tagged. Applications will use this instead of the
> Root_Connection_Type. It has the following data:
> 
> * Smart pointer to Root_Connection_Type'Class. This is dynamically
>   allocated when the connection is created.
> 
> It has the following methods:
> 
>   * Connect method takes a string, which is the connection URL.  Note:
>     Two ways of implementing:

Ok, this makes sense because you don't know the type
of Connection_Type apriori. I generally favour Booch
components myself, which includes a smart pointer.

...

> 4. Modify Root_Query_Type class:
> 
>    New_Query is the only function that takes a *Database_Type*
>    parameter.
> 
>    The functions that use to require Root_Connection_Type now use the
>    smart pointer that was saved instead.
> 
>    Why not make the procedures abstract instead of having them raise
>    an Is_Abstract? This way the checks can be done at compile time.

Answer: I wanted to put some code at the top level so that I
wouldn't have to repeat it for every database. For some reason
the compiler wouldn't let me do it (perhaps I was missing
something). I would be happy to have this done, but I was
unable to make it so in practice. Maybe someone else can
figure it out.

>    Execute already returns exception if not connected.
> 
>    Add methods for obtaining and clearing status information. This
>    should be cached so if you execute two separate queries (in two
>    separate variables) on the same database, you will get two status
>    messages saved.

You have to be real careful here, because database products
like Sybase use callbacks and things can change. In fact, Sybase
was a monster to tame with its oodles of states and callbacks.

> I hope this helps explain what I said earlier... I believe this solves
> a number of concerns with the existing system in one go.

I'll try to respond more fully later on, but this seems to make
sense.

--
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg