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Posted by Jochem Maas on 09/14/05 12:33
Norbert Wenzel wrote:
> Hi,
>
> I'm using PHP5 and try to do something like this:
>
> I have a base class called 'Entry' and a child class called
> 'ExtendedEntry'. I want to read all Entries to a certain topic from a
> database.
>
> While constructing the EntryObject I would like to look if Entry is a
> simple Entry or an ExtendedEntry. I want the new object to be an
> ExtendedEntry - if possible - and otherwise to be an Entry.
>
> It was not possible to return the object in the __construct() function
> and it was not possible to reassign $this with code like
> $this = new ExtendedEntry()
> also in the __construct() function. And I tried to always generate an
> ExtendedEntry with a flag, that says it is really Extended and a
> typecast afterwards, but I wasn't able to typecast to another object by
> (Entry) $extEntry.
>
> Any suggestions how to solve this problem without writing a
> generateEntry() function, that looks into the database and then calls
> the correct class type?
no not really - although I would suggest to create a static member function
(method) in the base class that acts as the factory e.g:
class Entry
{
static public function create($key = array(), $type = null)
{
// $type could be used to force the type of class
// or specify a class for a new object (as opposed to
// an object created from existing database content
// $key could be used to pass the relevant primary key(s)
// in order to retrieve the relevant data. (leave empty to create
// a 'new' object?)
}
}
actually you might try looking into the delegation pattern which could offer an alternative
to a factory function (i.e. the object can make extra methods from contained/helper
classes available depending on the type of data retrieved)
>
> thanks in advance,
> Norbert
>
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