added some features to sortable_columns

init.rb

@@ -1,5 +1,11 @@
 require 'sortable_columns'
 require 'helpers/view_helpers'
+require 'helpers/active_record_base_methods'
 
 ActionController::Base.send(:include, SortableColumns)
-ActionView::Base.send(:include, SortableColumns::ViewHelpers)
+# allow sort_params to preserve existing params 
+# (minus standard params like  :controller, :action, etc )
+ApplicationController.send( :append_before_filter, :store_params)
+
+ActionView::Base.send(:include, SortableColumns::ViewHelpers)
+ActiveRecord::Base.send(:extend, SortableColumns::ActiveRecordBaseMethods)

lib/helpers/active_record_base_methods.rb

@@ -0,0 +1,10 @@
+module SortableColumns
+
+  module ActiveRecordBaseMethods
+    attr_accessor :sortable_methods
+
+    def sortable_instance_methods(methods)
+      @sortable_methods = methods.to_a
+    end
+  end
+end

lib/helpers/view_helpers.rb

@@ -3,21 +3,19 @@ module SortableColumns
   module ViewHelpers
 
     def sort_params(sortable, column)
-      raise ParameterError.new("Please provide a Class as your first param. Ex: sort_param(User, :created_at)") unless sortable.is_a?(Class)
-      raise ParameterError.new("#{sortable} has no column \"#{column}\".") unless sortable.column_names.include?(column.to_s)
-
+      SortableColumns.validate_params(sortable, :sort_by=>column)
       init_session unless session[:sortable_columns]
 
       if session[:sortable_columns][sortable.to_s.downcase.to_sym]
         if session[:sortable_columns][sortable.to_s.downcase.to_sym][column.to_sym] == "asc"
-          return { :sort_by => column.to_s, :order => 'desc' }
+          return params.merge( { :sort_by => column.to_s, :order => 'desc' } )
         else
-          return { :sort_by => column.to_s, :order => 'asc' }  
+          return params.merge( { :sort_by => column.to_s, :order => 'asc' }  )
         end
       end
 
       # default
-      return { :sort_by => column.to_s, :order => 'desc' }
+      return params.merge( { :sort_by => column.to_s, :order => 'desc' } )
     end
 
   private

lib/sortable_columns.rb

@@ -4,9 +4,9 @@ class ParameterError < StandardError; end
 
   def sortable_order(sortable, options = {})
     if params[:sort_by] && params[:order]
-      validate_params(sortable)
+      validate_params(sortable, params)
       store_sort(sortable)
-      return "#{params.delete(:sort_by)} #{params.delete(:order)}"
+      return "#{params[:sort_by]} #{params[:order]}"
     else
       if session[:sortable_columns] && session[:sortable_columns][sortable.to_s.downcase.to_sym]
         column = session[:sortable_columns][sortable.to_s.downcase.to_sym].keys.first
@@ -17,12 +17,25 @@ def sortable_order(sortable, options = {})
     end
   end
 
-private
-
-  def validate_params(sortable)
-    raise ParameterError.new("#{sortable} has no column \"#{params[:sort_by]}\".") unless sortable.column_names.include?(params[:sort_by])
-    raise ParameterError.new("Order must be \"asc\" or \"desc\"") unless params[:order] == "asc" || params[:order] == "desc"
+  def sortable_attributes_and_methods( sortable )
+    columns = sortable.column_names
+    columns += sortable.sortable_methods.to_a if sortable.respond_to?( :sortable_methods )
+    columns.map{ |c| c.to_s }
+  end
+
+  def validate_params(sortable, params)
+    raise ParameterError.new("#{sortable} has no column or sortable_method \"#{params[:sort_by]}\". \n\nIf you're trying to sort by an instance method that isn't a column name (e.g. a value from an associated table), you must define \n\n\tsortable_instance_methods :my_method_1, :my_method_2 \n\nin your model class. Don't forget to include it as a column in your query too!") unless SortableColumns.sortable_attributes_and_methods(sortable).include?(params[:sort_by].to_s)
+    raise ParameterError.new("Order must be \"asc\" or \"desc\" - you gave #{params[:order]}") unless params[:order].blank? || ["asc","desc"].include?(params[:order].to_s.downcase)
+  end
+
+
+  def store_params
+    @params = params.clone - [ :controller, :action, :authenticity_token, :page, :format, :per_page ]
   end
+
+  module_function :sortable_attributes_and_methods, :validate_params
+
+private
 
   def store_sort(sortable)
     session[:sortable_columns] ||= Hash.new