Add an :update_only option to accepts_nested_attributes_for for to-on…

…e associations. [#2563 state:resolved]

Signed-off-by: Eloy Duran <eloy.de.enige@gmail.com>

activerecord/lib/active_record/nested_attributes.rb

@@ -212,6 +212,11 @@ module ClassMethods
       #   nested attributes array exceeds the specified limit, NestedAttributes::TooManyRecords
       #   exception is raised. If omitted, any number associations can be processed.
       #   Note that the :limit option is only applicable to one-to-many associations.
+      # [:update_only]
+      #   Allows to specify that the an existing record can only be updated.
+      #   A new record in only created when there is no existing record. This
+      #   option only works for on-to-one associations and is ignored for
+      #   collection associations. This option is off by default.
       #
       # Examples:
       #   # creates avatar_attributes=
@@ -221,9 +226,9 @@ module ClassMethods
       #   # creates avatar_attributes= and posts_attributes=
       #   accepts_nested_attributes_for :avatar, :posts, :allow_destroy => true
       def accepts_nested_attributes_for(*attr_names)
-        options = { :allow_destroy => false }
+        options = { :allow_destroy => false, :update_only => false }
         options.update(attr_names.extract_options!)
-        options.assert_valid_keys(:allow_destroy, :reject_if, :limit)
+        options.assert_valid_keys(:allow_destroy, :reject_if, :limit, :update_only)
 
         attr_names.each do |association_name|
           if reflection = reflect_on_association(association_name)
@@ -288,14 +293,29 @@ def _delete #:nodoc:
     # record’s id, then the existing record will be modified. Otherwise a new
     # record will be built.
     #
+    # If update_only is true, a new record is only created when no object exists,
+    # otherwise it will be updated
+    #
+    # If update_only is false and the given attributes include an <tt>:id</tt>
+    # that matches the existing record’s id, then the existing record will be
+    # modified. Otherwise a new record will be built.
+    #
     # If the given attributes include a matching <tt>:id</tt> attribute _and_ a
     # <tt>:_destroy</tt> key set to a truthy value, then the existing record
     # will be marked for destruction.
     def assign_nested_attributes_for_one_to_one_association(association_name, attributes)
       options = self.nested_attributes_options[association_name]
       attributes = attributes.with_indifferent_access
 
-      if attributes['id'].blank?
+      if options[:update_only]
+        if existing_record = send(association_name)
+          assign_to_or_mark_for_destruction(existing_record, attributes, options[:allow_destroy])
+        else
+          unless reject_new_record?(association_name, attributes)
+            send("build_#{association_name}", attributes.except(*UNASSIGNABLE_KEYS))
+          end
+        end
+      elsif attributes['id'].blank?
         unless reject_new_record?(association_name, attributes)
           method = "build_#{association_name}"
           if respond_to?(method)

activerecord/test/cases/nested_attributes_test.rb

@@ -245,6 +245,37 @@ def test_should_not_destroy_the_associated_model_until_the_parent_is_saved
   def test_should_automatically_enable_autosave_on_the_association
     assert Pirate.reflect_on_association(:ship).options[:autosave]
   end
+
+  def test_should_accept_update_only_option
+    Pirate.accepts_nested_attributes_for :ship, :update_only => true
+    @pirate.update_attribute(:ship_attributes, { :id => @pirate.ship.id, :name => 'Mayflower' })
+
+    Pirate.accepts_nested_attributes_for :ship, :allow_destroy => true, :reject_if => proc { |attributes| attributes.empty? }
+  end
+
+  def test_should_create_new_model_when_nothing_is_there_and_update_only_is_true
+    Pirate.accepts_nested_attributes_for :ship, :update_only => true
+    @ship.delete
+
+    assert_difference('Ship.count', 1) do
+      @pirate.reload.update_attribute(:ship_attributes, { :name => 'Mayflower' })
+    end
+
+    Pirate.accepts_nested_attributes_for :ship, :allow_destroy => true, :reject_if => proc { |attributes| attributes.empty? }
+  end
+
+
+  def test_should_update_existing_when_update_only_is_true_and_no_id_is_given
+    Pirate.accepts_nested_attributes_for :ship, :update_only => true
+
+    assert_no_difference('Ship.count') do
+      @pirate.reload.update_attributes(:ship_attributes => { :name => 'Mayflower' })
+    end
+
+    assert_equal 'Mayflower', @ship.reload.name
+
+    Pirate.accepts_nested_attributes_for :ship, :allow_destroy => true, :reject_if => proc { |attributes| attributes.empty? }
+  end
 end
 
 class TestNestedAttributesOnABelongsToAssociation < ActiveRecord::TestCase