Providing support for :inverse_of as an option to associations.

You can now add an :inverse_of option to has_one, has_many and belongs_to associations.  This is best described with an example:

class Man < ActiveRecord::Base
  has_one :face, :inverse_of => :man
end

class Face < ActiveRecord::Base
  belongs_to :man, :inverse_of => :face
end

m = Man.first
f = m.face

Without :inverse_of m and f.man would be different instances of the same object (f.man being pulled from the database again).  With these new :inverse_of options m and f.man are the same in memory instance.

Currently :inverse_of supports has_one and has_many (but not the :through variants) associations.  It also supplies inverse support for belongs_to associations where the inverse is a has_one and it's not a polymorphic.

Signed-off-by: Murray Steele <muz@h-lame.com>
Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

1 files changed, 9 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 2115878e32..0952b087d1 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1,4 +1,10 @@
 module ActiveRecord
+  class InverseOfAssociationNotFoundError < ActiveRecordError #:nodoc:
+    def initialize(reflection)
+      super("Could not find the inverse association for #{reflection.name} (#{reflection.options[:inverse_of].inspect} in #{reflection.class_name})")
+    end
+  end
+
   class HasManyThroughAssociationNotFoundError < ActiveRecordError #:nodoc:
     def initialize(owner_class_name, reflection)
       super("Could not find the association #{reflection.options[:through].inspect} in model #{owner_class_name}")
@@ -1488,7 +1494,7 @@ module ActiveRecord
           :finder_sql, :counter_sql,
           :before_add, :after_add, :before_remove, :after_remove,
           :extend, :readonly,
-          :validate
+          :validate, :inverse_of
         ]
 
         def create_has_many_reflection(association_id, options, &extension)
@@ -1502,7 +1508,7 @@ module ActiveRecord
         @@valid_keys_for_has_one_association = [
           :class_name, :foreign_key, :remote, :select, :conditions, :order,
           :include, :dependent, :counter_cache, :extend, :as, :readonly,
-          :validate, :primary_key
+          :validate, :primary_key, :inverse_of
         ]
 
         def create_has_one_reflection(association_id, options)
@@ -1521,7 +1527,7 @@ module ActiveRecord
         @@valid_keys_for_belongs_to_association = [
           :class_name, :foreign_key, :foreign_type, :remote, :select, :conditions,
           :include, :dependent, :counter_cache, :extend, :polymorphic, :readonly,
-          :validate, :touch
+          :validate, :touch, :inverse_of
         ]
 
         def create_belongs_to_reflection(association_id, options)