use persisted? instead of new_record? wherever possible

- persisted? is the API defined in ActiveModel
- makes it easier for extension libraries to conform to ActiveModel APIs
  without concern for whether the extended object is specifically
  ActiveRecord

[#5927 state:committed]

Signed-off-by: Santiago Pastorino <santiago@wyeworks.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 82d94b848a..75ae06f5e9 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -3,10 +3,11 @@ module ActiveRecord
     module PrimaryKey
       extend ActiveSupport::Concern
 
-      # Returns this record's primary key value wrapped in an Array
-      # or nil if the record is a new_record?
+      # Returns this record's primary key value wrapped in an Array or nil if
+      # the record is not persisted? or has just been destroyed.
       def to_key
-        new_record? ? nil : [ id ]
+        key = send(self.class.primary_key)
+        [key] if key
       end
 
       module ClassMethods