Cache nil results for :included has_one associations also. Closes #5787.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4783 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

 *SVN*
 
-* Fixed a bug which would cause .save to fail after trying to access a empty has_one association on a unsaved record. [Tobias Luetke] 
+* Cache nil results for :included has_one associations also.  #5787 [Michael Schoen]
+
+* Fixed a bug which would cause .save to fail after trying to access a empty has_one association on a unsaved record. [Tobias Luetke]
 
 * Nested classes are given table names prefixed by the singular form of the parent's table name. [Jeremy Kemper]
     Example: Invoice::Lineitem is given table name invoice_lineitems

activerecord/lib/active_record/associations.rb

@@ -870,7 +870,7 @@ def association_accessor_methods(reflection, association_proxy_class)
           end
 
           define_method("set_#{reflection.name}_target") do |target|
-            return if target.nil?
+            return if target.nil? and association_proxy_class == BelongsToAssociation
             association = association_proxy_class.new(self, reflection)
             association.target = target
             instance_variable_set("@#{reflection.name}", association)
@@ -1311,11 +1311,15 @@ def construct_association(record, join, row)
                 when :has_many, :has_and_belongs_to_many
                   collection = record.send(join.reflection.name)
                   collection.loaded
-    
+
                   return nil if record.id.to_s != join.parent.record_id(row).to_s or row[join.aliased_primary_key].nil?
                   association = join.instantiate(row)
                   collection.target.push(association) unless collection.target.include?(association)
-                when :has_one, :belongs_to
+                when :has_one
+                  return if record.id.to_s != join.parent.record_id(row).to_s
+                  association = join.instantiate(row) unless row[join.aliased_primary_key].nil?
+                  record.send("set_#{join.reflection.name}_target", association)
+                when :belongs_to
                   return if record.id.to_s != join.parent.record_id(row).to_s or row[join.aliased_primary_key].nil?
                   association = join.instantiate(row)
                   record.send("set_#{join.reflection.name}_target", association)

activerecord/test/associations_test.rb

@@ -99,6 +99,9 @@ def test_has_one
   def test_has_one_cache_nils
     assert_nil companies(:another_firm).account
     assert_queries(0) { companies(:another_firm).account }
+
+    firms = Firm.find(:all, :include => :account)
+    assert_queries(0) { firms.each(&:account) }
   end
 
   def test_proxy_assignment