Re: Any more thoughts on the LIMIT/extra SQL issue?

[prev] [thread] [next] [Date index for 2004/07/30]

Here's a quick patch which converts the current order_by functionality
to "handlers" as I suggested earlier.  There are some commented out
lines where I was going to add a distinct_on handler until I realized
how difficult (I think) it is to get at the "SELECT ..." part of the
SQL due to the Ima::DBI closure.  "DISTINCT ON" functionality is
something I use pretty regularly and have to add in as new search_*
methods normally.  It would be nice to be able to add this
functionality as a plugin that works with regular searches.

This is meant just for discussion - I wouldn't suggest using this
code, though it does pass all the current tests.  The current patch
croaks on unhandled $search_opts.  There's stuff that could be added
to this such as more specific ordering (assign each handler an order
number?) if people think it's a good idea to go down this road.

Todd
--
Todd Holbrook
Systems Consultant
Simon Fraser University Library

Patch to Class/DBI.pm:

104a105
> __PACKAGE__->mk_classdata('__search_handlers');
1091,1092c1092,1100
<       $frag .= " ORDER BY $search_opts->{order_by}"
<               if $search_opts->{order_by};
---
> 
>       foreach my $handler (@{$class->__search_handlers}) {
>               &$handler(\$frag, $search_opts);
>       }
> 
>       if (scalar(keys(%{$search_opts}))) {
>               $class->_croak("Not all search_opts were handled: ", join ',', keys(%{$search_opts}));
>       }
> 
1097a1106,1154
> 
> sub append_search_handler {
>       my ($class, $handler) = @_;
> 
>       my $handlers = $class->__search_handlers;
>       push @$handlers, $handler;
>       $class->__search_handlers($handlers);
> 
>       return $class;
> }
> 
> sub prepend_search_handler {
>       my ($class, $handler) = @_;
> 
>       my $handlers = $class->__search_handlers;
>       unshift @$handlers, $handler;
>       $class->__search_handlers($handlers);
> 
>       return $class;
> }
> 
> 
> sub _search_handler_order_by {
>       my ($frag_ref, $search_opts) = @_;
> 
>       if ($search_opts->{order_by}) {
>               $$frag_ref .= " ORDER BY $search_opts->{order_by}";
>               delete $search_opts->{order_by};
>       }
> 
>       return 1;
> }
> 
> #sub _search_handler_distinct_on {
> #     my ($frag_ref, $search_opts) = @_;
> #
> #     if ($search_opts->{distinct_on}) {
> #             my $distinct = "DISTINCT ON ($search_opts->{distinct_on}) ";
> #             $$frag_ref =~ s/SELECT\s+/SELECT $distinct/;
> #             delete $search_opts->{distinct_on};
> #     }
> #
> #     return 1;
> #}
> 
> __PACKAGE__->append_search_handler(\&_search_handler_order_by);
> #__PACKAGE__->prepend_search_handler(\&_search_handler_distinct_on);
> 
>