1 files changed, 49 insertions, 17 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index aeca74ef4a..baad8fc5fd 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -42,11 +42,12 @@ module ActiveRecord
     end
   end
 
-  class HasManyThroughCantAssociateThroughHasManyReflection < ActiveRecordError #:nodoc:
+  class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ActiveRecordError #:nodoc:
     def initialize(owner, reflection)
       super("Cannot modify association '#{owner.class.name}##{reflection.name}' because the source reflection class '#{reflection.source_reflection.class_name}' is associated to '#{reflection.through_reflection.class_name}' via :#{reflection.source_reflection.macro}.")
     end
   end
+
   class HasManyThroughCantAssociateNewRecords < ActiveRecordError #:nodoc:
     def initialize(owner, reflection)
       super("Cannot associate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to create the has_many :through record associating them.")
@@ -416,6 +417,32 @@ module ActiveRecord
     #   @firm.clients.collect { |c| c.invoices }.flatten # select all invoices for all clients of the firm
     #   @firm.invoices                                   # selects all invoices by going through the Client join model.
     #
+    # Similarly you can go through a +has_one+ association on the join model:
+    #
+    #   class Group < ActiveRecord::Base
+    #     has_many   :users
+    #     has_many   :avatars, :through => :users
+    #   end
+    #
+    #   class User < ActiveRecord::Base
+    #     belongs_to :group
+    #     has_one    :avatar
+    #   end
+    #
+    #   class Avatar < ActiveRecord::Base
+    #     belongs_to :user
+    #   end
+    #
+    #   @group = Group.first
+    #   @group.users.collect { |u| u.avatar }.flatten # select all avatars for all users in the group
+    #   @group.avatars                                # selects all avatars by going through the User join model.
+    #
+    # An important caveat with going through +has_one+ or +has_many+ associations on the join model is that these associations are
+    # *read-only*.  For example, the following would not work following the previous example:
+    #
+    #   @group.avatars << Avatar.new                # this would work if User belonged_to Avatar rather than the other way around.
+    #   @group.avatars.delete(@group.avatars.last)  # so would this
+    #
     # === Polymorphic Associations
     #
     # Polymorphic associations on models are not restricted on what types of models they can be associated with.  Rather, they
@@ -819,7 +846,7 @@ module ActiveRecord
       # [:through]
       #   Specifies a Join Model through which to perform the query.  Options for <tt>:class_name</tt> and <tt>:foreign_key</tt>
       #   are ignored, as the association uses the source reflection. You can only use a <tt>:through</tt> query through a <tt>belongs_to</tt>
-      #   or <tt>has_many</tt> association on the join model.
+      #   <tt>has_one</tt> or <tt>has_many</tt> association on the join model.
       # [:source]
       #   Specifies the source association name used by <tt>has_many :through</tt> queries.  Only use it if the name cannot be
       #   inferred from the association.  <tt>has_many :subscribers, :through => :subscriptions</tt> will look for either <tt>:subscribers</tt> or
@@ -1367,7 +1394,7 @@ module ActiveRecord
 
             define_method("#{reflection.name.to_s.singularize}_ids=") do |new_value|
               ids = (new_value || []).reject { |nid| nid.blank? }
-              send("#{reflection.name}=", reflection.class_name.constantize.find(ids))
+              send("#{reflection.name}=", reflection.klass.find(ids))
             end
           end
         end
@@ -1656,7 +1683,7 @@ module ActiveRecord
           relation.join(joins)
 
           relation.where(construct_conditions(options[:conditions], scope))
-          relation.where(construct_arel_limited_ids_condition(options, join_dependency)) if join_dependency && !using_limitable_reflections?(join_dependency.reflections) && ((scope && scope[:limit]) || options[:limit])
+          relation.where(construct_arel_limited_ids_condition(options, join_dependency)) if !using_limitable_reflections?(join_dependency.reflections) && ((scope && scope[:limit]) || options[:limit])
 
           relation.project(column_aliases(join_dependency))
           relation.group(construct_group(options[:group], options[:having], scope))
@@ -1685,18 +1712,23 @@ module ActiveRecord
         end
 
         def construct_finder_sql_for_association_limiting(options, join_dependency)
-          # Only join tables referenced in order or conditions since this is particularly slow on the pre-query.
-          tables_from_conditions = conditions_tables(options)
-          tables_from_order      = order_tables(options)
-          all_tables             = tables_from_conditions + tables_from_order
-          options[:joins] = all_tables.uniq.map {|table|
-            join_dependency.joins_for_table_name(table)
-          }.flatten.compact.uniq.collect { |assoc| assoc.association_join }.join
-
-          construct_finder_sql(options.merge(
-            :select => connection.distinct("#{connection.quote_table_name table_name}.#{primary_key}", construct_order(options[:order], scope(:find)).join(","))
-            )
-          )
+          scope = scope(:find)
+
+          relation = arel_table(options[:from])
+
+          joins = join_dependency.join_associations.collect{|join| join.association_join }.join
+          joins << construct_join(options[:joins], scope)
+          relation.join(joins)
+
+          relation.where(construct_conditions(options[:conditions], scope))
+          relation.project(connection.distinct("#{connection.quote_table_name table_name}.#{primary_key}", construct_order(options[:order], scope(:find)).join(",")))
+
+          relation.group(construct_group(options[:group], options[:having], scope))
+          relation.order(construct_order(options[:order], scope))
+          relation.take(construct_limit(options[:limit], scope))
+          relation.skip(construct_limit(options[:offset], scope))
+
+          sanitize_sql(relation.to_sql)
         end
 
         def tables_in_string(string)
@@ -1870,7 +1902,7 @@ module ActiveRecord
                     descendant
                   end.flatten.compact
 
-                  remove_duplicate_results!(reflection.class_name.constantize, parent_records, associations[name]) unless parent_records.empty?
+                  remove_duplicate_results!(reflection.klass, parent_records, associations[name]) unless parent_records.empty?
                 end
             end
           end