Not need to pass join attributes to association build

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -73,7 +73,9 @@ def through_association
         # association
         def build_through_record(record)
           @through_records[record.object_id] ||= begin
-            through_record = through_association.build(construct_join_attributes(record))
+            ensure_mutable
+
+            through_record = through_association.build
             through_record.send("#{source_reflection.name}=", record)
             through_record
           end

activerecord/lib/active_record/associations/through_association.rb

@@ -37,9 +37,7 @@ def target_scope
         # situation it is more natural for the user to just create or modify their join records
         # directly as required.
         def construct_join_attributes(*records)
-          if source_reflection.macro != :belongs_to
-            raise HasManyThroughCantAssociateThroughHasOneOrManyReflection.new(owner, reflection)
-          end
+          ensure_mutable
 
           join_attributes = {
             source_reflection.foreign_key =>
@@ -73,6 +71,12 @@ def foreign_key_present?
           !owner[through_reflection.foreign_key].nil?
         end
 
+        def ensure_mutable
+          if source_reflection.macro != :belongs_to
+            raise HasManyThroughCantAssociateThroughHasOneOrManyReflection.new(owner, reflection)
+          end
+        end
+
         def ensure_not_nested
           if reflection.nested?
             raise HasManyThroughNestedAssociationsAreReadonly.new(owner, reflection)

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -4,7 +4,6 @@
 require 'models/reference'
 require 'models/job'
 require 'models/reader'
-require 'models/secure_reader'
 require 'models/comment'
 require 'models/tag'
 require 'models/tagging'
@@ -60,7 +59,7 @@ def test_associate_existing
   end
 
   def test_associate_existing_with_strict_mass_assignment_sanitizer
-    ActiveRecord::Base.mass_assignment_sanitizer = :strict
+    SecureReader.mass_assignment_sanitizer = :strict
 
     SecureReader.new
 
@@ -71,7 +70,7 @@ def test_associate_existing_with_strict_mass_assignment_sanitizer
       post.secure_people << person
     end
   ensure
-    ActiveRecord::Base.mass_assignment_sanitizer = :logger
+    SecureReader.mass_assignment_sanitizer = :logger
   end
 
   def test_associate_existing_record_twice_should_add_to_target_twice

activerecord/test/models/reader.rb

@@ -3,3 +3,12 @@ class Reader < ActiveRecord::Base
   belongs_to :person, :inverse_of => :readers
   belongs_to :single_person, :class_name => 'Person', :foreign_key => :person_id, :inverse_of => :reader
 end
+
+class SecureReader < ActiveRecord::Base
+  self.table_name = "readers"
+
+  belongs_to :secure_post, :class_name => "Post", :foreign_key => "post_id"
+  belongs_to :secure_person, :inverse_of => :secure_readers, :class_name => "Person", :foreign_key => "person_id"
+
+  attr_accessible nil
+end