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Posted by OmegaJunior on 02/22/07 23:40
On Thu, 22 Feb 2007 17:44:47 +0100, Andrew <Taylor> wrote:
> Hi,
>
> I've been using PHP for a long time, I have designed and developed a =
> number of mid-range systems. I've always used a procedural approach. I=
=
> fully understand the concept of OO, I know all the basics and I know h=
ow =
> to code OO. What I'm having problems with is understanding how to =
> design/architect projects using OO.
>
> Can anyone reccomend any good online tutorials / online learning / vid=
eo =
> tutorials which deal with these subjects specifically in PHP. I have a=
=
> number of the class OO books which help me understand the principals, =
=
> but, not how to leverage those principals in to system design.
>
> Also, I am trying to learn how to do this myself, this is not just a =
> lazy call for the answer, perhaps somebody could answer this which mig=
ht =
> help me on my way as well as the above request for further information=
..
>
> One thing which confuses me is how to use databases in the OO approach=
.. =
> Imagine we have a system which deals with music CDs:
>
> class MusicCD {
>
> private $title;
> private $artist;
>
> function __constructor($title, $artist) {
>
> $this->title =3D $title;
> $this->artist =3D $artist;
> }
>
> function displayCD() {
>
> echo $this->title.' '.$this->artist;
> }
> }
>
> Now, we want to save this information in to a database, what is the =
> correct way (best practice) for doing this; is it to create a saveCD =
> method in my musicCD class? Should this method expect a database objec=
t =
> to be passed in, or, should it call static methods of another class?
>
> function saveCD(Database $databaseObject) {
>
> $databaseObject->query('INSERT INTO...
> }
>
> function saveCD() {
>
> mysql_connect(...)
> }
>
> Surely in the OO concept the MusicCD class doesn't need to know about =
my =
> table structure etc, would this be a case for a MusicCDDatabase class =
=
> which knows about MusicCD and DB?
>
> Just to re-itterate, I know how to code in PHP, I know how to use OO =
> syntax, I'm just having problems designing my system.
>
> Thanks for reading a long post, and thanks in advance for any help.
>
> Andrew
>
Interesting question, Andrew! (And I'm not just saying that because we'r=
e =
name-sakes ;) )
I was discussing a similar topic with one of my colleagues at work:
where does the user interface come in?
And we found two approaches:
1) The interface is defined separately, either using O.O. techniques or =
=
not, and gets told about the O.O. system in design time. Then the user =
chooses some functionality, which in turn invokes the O.O. instances.
2) The O.O. system is told that for some methods it needs a user =
interface, thus the instance constructors accept parameters that indicat=
e =
which parts of an existing user interface belongs to which method. Then =
=
when the user chooses some functionality, it's the O.O. instance that =
invokes the user interface.
Something similar can be conceived with database access:
The class needs to know when it needs to save anything... but not =
necessarily where or how. So you could design a helper class and offload=
=
the actual database interaction to an instance thereof, or you could hav=
e =
your MusicCD class inherit and extend a database-capable class. That way=
=
you could derive a MusicCD class from an OracleSQL class, or from a MySQ=
L =
class, or from a Text class... or all of them combined, choosing which t=
o =
use during run-time, based on some configuration.
-- =
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