1 files changed, 60 insertions, 17 deletions

diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 99c0e71f97..f8dffce2f1 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -138,6 +138,10 @@ module ActiveRecord
     #       PolymorphicReflection
     #         RuntimeReflection
     class AbstractReflection # :nodoc:
+      def through_reflection?
+        false
+      end
+
       def table_name
         klass.table_name
       end
@@ -239,6 +243,10 @@ module ActiveRecord
       def alias_candidate(name)
         "#{plural_name}_#{name}"
       end
+
+      def chain
+        collect_join_chain
+      end
     end
 
     # Base class for AggregateReflection and AssociationReflection. Objects of
@@ -421,7 +429,7 @@ module ActiveRecord
 
       # A chain of reflections from this one back to the owner. For more see the explanation in
       # ThroughReflection.
-      def chain
+      def collect_join_chain
         [self]
       end
 
@@ -441,6 +449,10 @@ module ActiveRecord
         scope ? [[scope]] : [[]]
       end
 
+      def has_scope?
+        scope
+      end
+
       def has_inverse?
         inverse_name
       end
@@ -495,6 +507,18 @@ module ActiveRecord
       VALID_AUTOMATIC_INVERSE_MACROS = [:has_many, :has_one, :belongs_to]
       INVALID_AUTOMATIC_INVERSE_OPTIONS = [:conditions, :through, :polymorphic, :foreign_key]
 
+      def add_as_source(seed)
+        seed
+      end
+
+      def add_as_polymorphic_through(reflection, seed)
+        seed + [PolymorphicReflection.new(self, reflection)]
+      end
+
+      def add_as_through(seed)
+        seed + [self]
+      end
+
       protected
 
         def actual_source_reflection # FIXME: this is a horrible name
@@ -684,6 +708,10 @@ module ActiveRecord
         @source_reflection_name = delegate_reflection.options[:source]
       end
 
+      def through_reflection?
+        true
+      end
+
       def klass
         @klass ||= delegate_reflection.compute_class(class_name)
       end
@@ -742,25 +770,13 @@ module ActiveRecord
       #   # => [<ActiveRecord::Reflection::ThroughReflection: @delegate_reflection=#<ActiveRecord::Reflection::HasManyReflection: @name=:tags...>,
       #         <ActiveRecord::Reflection::HasManyReflection: @name=:taggings, @options={}, @active_record=Post>]
       #
-      def chain
-        @chain ||= begin
-          a = source_reflection.chain
-          b = through_reflection.chain.map(&:dup)
-
-          if options[:source_type]
-            b[0] = PolymorphicReflection.new(b[0], self)
-          end
-
-          chain = a + b
-          chain[0] = self # Use self so we don't lose the information from :source_type
-          chain
-        end
+      def collect_join_chain
+        collect_join_reflections [self]
       end
 
       # This is for clearing cache on the reflection. Useful for tests that need to compare
       # SQL queries on associations.
       def clear_association_scope_cache # :nodoc:
-        @chain = nil
         delegate_reflection.clear_association_scope_cache
         source_reflection.clear_association_scope_cache
         through_reflection.clear_association_scope_cache
@@ -807,13 +823,19 @@ module ActiveRecord
         end
       end
 
+      def has_scope?
+        scope || options[:source_type] ||
+          source_reflection.has_scope? ||
+          through_reflection.has_scope?
+      end
+
       def join_keys(association_klass)
         source_reflection.join_keys(association_klass)
       end
 
       # A through association is nested if there would be more than one join table
       def nested?
-        chain.length > 2
+        source_reflection.through_reflection? || through_reflection.through_reflection?
       end
 
       # We want to use the klass from this reflection, rather than just delegate straight to
@@ -913,6 +935,27 @@ module ActiveRecord
         scope_chain
       end
 
+      def add_as_source(seed)
+        collect_join_reflections seed
+      end
+
+      def add_as_polymorphic_through(reflection, seed)
+        collect_join_reflections(seed + [PolymorphicReflection.new(self, reflection)])
+      end
+
+      def add_as_through(seed)
+        collect_join_reflections(seed + [self])
+      end
+
+      def collect_join_reflections(seed)
+        a = source_reflection.add_as_source seed
+        if options[:source_type]
+          through_reflection.add_as_polymorphic_through self, a
+        else
+          through_reflection.add_as_through a
+        end
+      end
+
       protected
 
         def actual_source_reflection # FIXME: this is a horrible name
@@ -969,7 +1012,7 @@ module ActiveRecord
       end
 
       def constraints
-        [source_type_info]
+        @reflection.constraints + [source_type_info]
       end
 
       def source_type_info