using :param_name => "something[page]" leads to invalid behavior

Problem

If I use a compound parameter name for :param_name, like this:

   will_paginate(resultset, :param_name => "test[page]")

After a couple of clicks on page links in the pagination panel it gets stuck on one page, no matter where you click

Why

will_paginate preserves GET parameters for page links (which is cool). This is done in view_helpers.rb :

    def url_options(page)
      options = { param_name => page }
      # page links should preserve GET parameters
      options = params.merge(options) if @template.request.get?
      options.rec_merge!(@options[:params]) if @options[:params]
      return options
    end

The problem is that with a parameter name like test[page] before merging optons and params the options has is

  {:"test[page]"=>1}

while params also contain this parameter if the user has already clicked once on a page link, but it's parsed into a hash of hashes:

  {:action=>"index", :controller=>"dashboards", :test=>{"page"=>"2"}}

Consequently, params.merge(options) does not overwrite :test=>{"page"=>"2"}, the resulting merged hash is

  {:test=>{"page"=>"2"}, :action=>"index", :controller=>"dashboards", :"test[page]"=>1}

and in the URL the page parameter is repeated twice:

?test%5Bpage%5D=1&test%5Bpage%5D=2

Solution

I fixed it with the following code:

  def url_options(page)
    options = ActionController::AbstractRequest.parse_query_parameters("#{param_name}=#{page}")
    options.keys.each do |key| # convert keys to symbols
      options[key.intern] = options[key]
      options.delete(key)
    end
    # page links should preserve GET parameters
    options = params.merge(options) if @template.request.get?
    options.rec_merge!(@options[:params]) if @options[:params]
    return options
  end

There might be a more elegant way, but this one works .