use Perl

• Re: Ask use.perl.org - Class Tree + Driver API ? (Score:1)

  by cosimo (4138) <cosimo@cpan.org> on 2007.05.29 14:23 (#55315) Homepage Journal

  Hi Alias,

  I don't know if I understood completely what you are trying to accomplish, but I think I have developed a similar system, that is used to access different data sources (txt, ftp, http, sql, AS/400, ...) with a single interface. Sql class in particular has the behaviour you mention, in that it supports Postgres, Mysql, Oracle, DB2, Sybase, Informix, ...

  In my case, I have a "Driver" class with many subclasses like Pg, Oracle, Sybase, MSSQL, ... that are embedded in a $self->{driver} member.

  When I need to specialize behaviour for (example) Postgres, I never test for driver name, but rather for a special "feature" (missing or implemented) by the database.

  An example is worth 1000 words:

  sub get_first_10_records
  {
      my $self = $_[0];
  
      # Get underlying driver class (don't care if Pg, Mysql, ...)
      my $drv  = $self->driver();
      my $sql  = 'SELECT * FROM hgttg';
      my $has_ph = $drv->supports('placeholders');
      my $has_limit = $drv->supports('limit');
  
      if($has_ph)
      {
          $sql .= ' WHERE answer=?';
      }
      else
      {
          $sql .= ' WHERE answer=42';
      }
  
      if($has_limit)
      {
          $sql .= ' LIMIT 10';
      }
  
      my @recs = $self->fire_query($sql, 42);
  
      if(!$has_limit)
      {
         @recs = splice(@recs, 0, 10);
      }
  
      return(\@recs);
  }

  Don't get me wrong. This example is not very exciting, but I think the concept behind is interesting. Checking for features *across* all driver classes, creating a "common denominator" approach, rather than specializing by class.

  Sorry if I have totally missed the point... :-)

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