inheriting from DBIx::Recordset

[alan milligan <al...@hotmail.com>]

Hi,

Hope this question has not been asked before, but I want to implement a 
layer over top of DBIx::Recordset that basically gives me something similar 
to the java.sql.DatabaseMetaData class.

A simple design is just to create a MyMetaData object and create a class 
built above DBx::Recordset to override a couple of functions and do the 
DBIx::Recordset call then do the additional stuff to populate the MyMetaData 
object.

However, if I do:

package MyRecordset;
@ISA =qw(DBIx::Recordset);
1;

package main;
*set = MyRecordset->Search({'!Table'      => 'blabla'});

...

I get this unfortunate effect of "Need DBIx::Recordset or setup parameter "

This is because there are a few places in the Setup functions of 
DBIx::Recordset which directly test the object type :

    elsif (ref ($arg) eq 'DBIx::Recordset')


This effectively precludes good behaviour for derived objects which will not 
be blessed to DBIx::Recordset.

I have had to hack this stuff in DBIx::Recordset to make my class known, but 
would prefer that this constraint was lifted from DBIx::Recordset.

For example, if the type returned from ref($arg) is a REF then go ahead and 
do the assignment - if later things prove to be inconsistent then just maybe 
the punter should stick with the vanilla DBIx::Recordset...

Perl does not provide much natural language support for utilising classes 
(ie private constructors, pure virtual functions, un-overrideable functions 
etc etc), so it can be quite difficult to use inheritance to share code.  
Any thoughts are welcomed to working around this, and to any further 
pitfalls I may discover!

Cheers, Alan



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Re: inheriting from DBIx::Recordset

[Gerald Richter <ri...@ecos.de>]

> I get this unfortunate effect of "Need DBIx::Recordset or setup parameter
"
>
> This is because there are a few places in the Setup functions of
> DBIx::Recordset which directly test the object type :
>
>     elsif (ref ($arg) eq 'DBIx::Recordset')
>

We should trun this into

     elsif (ref ($arg) && $arg -> isa ('DBIx::Recordset'))

this is a little bit slower, but of course much more OO and should solve
your problem.

Gerald



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