Hoopla! » Making Will Paginate work with Scope Out

Hoopla! - now with extra whiz-bang home

Clearly I’m loving scope out. It’s dramatically reduced the amount and complexity of code for my current app. Another plugin I’ve come to love is will_paginate because of the very Ruby-like way it allows paginating without any configuration.

Unfortunately these two plugins don’t quite work together well. Like Rails itself will_paginate does a fine job of finding the records but is less reliable for counting them.

Example:

    class Person < ActiveRecord::Base
      scope_out :women, :conditions => ["people.sex = ?", 'F']
    end
    35.times do
      Person.create(:sex => 'F')
    end
    14.times do
      Person.create(:sex => 'M')
    end
    @people = Person.paginate_women(:all, :page => 2)
    @people.size # => 4
    @people.total_entries # => 49

Whoops. That makes for some confusing pagination.

There’s a few possibilities for fixing this. My favorite is to hope that Mislav can apply this patch. But in the meantime here’s a quick way around it:

    module WillPaginate
      module Finder
        module ClassMethods
          def wp_count_with_scope!(options, args, finder)
            if respond_to?(scoper = finder.sub(/^find/, 'with'))
            	send(scoper) { wp_count_without_scope!(options, args, finder) }
            else
              wp_count_without_scope!(options, args, finder)
            end
          end
          alias_method_chain :wp_count!, :scope
        end
      end
    end

Ted said: OK I've read it three times and I don't quite get it :-\ When you call "Person.paginate_women" what is scope_out (unpatched) doing behind the scenes? Looking for the method "find_women"? If so why isn't it finding it and why is it returning all the records? I'm lost :-(
Jack Danger said: You're really close Ted. Will Paginate translates paginate_women(:all) into find_women(:all) just fine. Then find_women(:all) triggers the scope_out method_missing that runs find(:all) inside the :women scope. And that process works fine. What's broken is that Will Paginate then calls plain old count() with the same conditions as passed to find - but it isn't executed inside a scope because it's not one of those magical methods that would get intercepted by scope_out's method_missing. So it can properly find all the right records but when it does it's counting query to come up with a total it's way, way off.
Jack Danger said: Wow. I even confused myself there. First of all - I just added Textile formatting to comments because these run on sentences of mine are bad enough. Second of all: paginate_women(:all) is turned into the following by will_paginate's method_missing: find_women(:all) # which is turned into the following by scope_out's method_missing: with_scope :find => {:conditions => ['people.sex = ?', 'F']} do find(:all) end But then to get a total number of entries to do the pagination links will_paginate calls: count(:all) which kills the Ruby magic.
Ted said: Thanks for the clarification :-)
Chris said: will_paginate and scope_out should now play nicely as of r326. Thanks for the post.
Jack Danger said: Thanks Chris!
Zubin said: They appear to be playing nicely until you add :per_page to the mix. eg this works: @pages = Page.paginate_all_approved :page => params[:page] but this doesn't: @pages = Page.paginate_all_approved :page => params[:page], :per_page => 5 The navigation links to non-existent pages (probably counting find(:all)?).

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