1 files changed, 44 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
new file mode 100644
index 0000000000..365fdeb55a
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -0,0 +1,44 @@
+module ActiveRecord
+  module AttributeMethods
+    module PrimaryKey
+      extend ActiveSupport::Concern
+
+      module ClassMethods
+        # Defines the primary key field -- can be overridden in subclasses. Overwriting will negate any effect of the
+        # primary_key_prefix_type setting, though.
+        def primary_key
+          reset_primary_key
+        end
+
+        def reset_primary_key #:nodoc:
+          key = get_primary_key(base_class.name)
+          set_primary_key(key)
+          key
+        end
+
+        def get_primary_key(base_name) #:nodoc:
+          key = 'id'
+          case primary_key_prefix_type
+            when :table_name
+              key = base_name.to_s.foreign_key(false)
+            when :table_name_with_underscore
+              key = base_name.to_s.foreign_key
+          end
+          key
+        end
+
+        # Sets the name of the primary key column to use to the given value,
+        # or (if the value is nil or false) to the value returned by the given
+        # block.
+        #
+        #   class Project < ActiveRecord::Base
+        #     set_primary_key "sysid"
+        #   end
+        def set_primary_key(value = nil, &block)
+          define_attr_method :primary_key, value, &block
+        end
+        alias :primary_key= :set_primary_key
+      end
+    end
+  end
+end