[Catalyst] TIP: resolv uri based on delta params

[N. Arakawa]

I often make a data-table view, which links to similar views with
small parameter changes, such as paging or sorting order.

In this case, making a link URI based on 'delta' information is handy.

In Application Code:
  sub uri_delta{
    my($self, at arg)=@_;
    if (@arg % 2 != 0){
      $self->log->error("Odd elements for a hash!");
      return "Odd elements for a hash!";
    }else{
      my %new_param = (%{$self->request->parameters}, @arg);
   # Which is better, 'parameters' or 'query_parameters' ?
      return $self->uri_for($self->action,\%new_param);
    }
  }

In TT-Template:
 <a href="[% Catalyst.uri_delta('page', prev); %]">&larr;</a>

There is at least one drawback of this approach:
 it is not possible to 'delete' a parameter.
However, assign 'undef' instead of deleting  parameter often enough.

-- 
 - N. Arakawa