limited eager loading patch

finder_methods.rb

diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index c6e8762..56985fa 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -226,16 +226,42 @@ module ActiveRecord
     end
 
     def apply_join_dependency(relation, join_dependency)
-      join_dependency.join_associations.each do |association|
-        relation = association.join_relation(relation)
-      end
-
       limitable_reflections = using_limitable_reflections?(join_dependency.reflections)
 
       if !limitable_reflections && relation.limit_value
-        limited_id_condition = construct_limited_ids_condition(relation.except(:select))
+		# Determine which tables are actually used to limit/sort the result set
+		order_tables = tables_in_string(relation.order_values.join(', ')).map {|t| t.strip if t.respond_to?(:strip)}
+		where_tables = tables_in_string(relation.arel.where_sql).map {|t| t.strip if t.respond_to?(:strip)}
+		all_tables = order_tables + where_tables
+		all_tables.uniq!
+
+		filtering_associations = join_dependency.join_associations.select{|ja| all_tables.include?(ja.aliased_table_name)}
+		all_table_names = filtering_associations.map do |fa|
+		  table_names = []
+		  node = fa
+		  while node.respond_to?(:parent)
+			table_names += node.tables.map(&:name)
+			node = node.parent
+		  end
+		  table_names << node.aliased_table_name
+		end.flatten.uniq
+
+		# Create a separate relation for use in the DISTINCT query
+		clean_relation = relation.dup
+		for association in join_dependency.join_associations
+		  if all_table_names.include?(association.aliased_table_name)
+			clean_relation = association.join_relation(clean_relation)
+		  end
+		  relation = association.join_relation(relation) 
+		end
+		
+        limited_id_condition = construct_limited_ids_condition(clean_relation.except(:select))
         relation = relation.where(limited_id_condition)
-      end
+	  else
+		join_dependency.join_associations.each do |association|
+		  relation = association.join_relation(relation)
+		end
+	  end
 
       relation = relation.except(:limit, :offset) unless limitable_reflections