1 files changed, 24 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/readonly_attributes.rb b/activerecord/lib/active_record/readonly_attributes.rb
new file mode 100644
index 0000000000..7bc26993d5
--- /dev/null
+++ b/activerecord/lib/active_record/readonly_attributes.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ReadonlyAttributes
+    extend ActiveSupport::Concern
+
+    included do
+      class_attribute :_attr_readonly, instance_accessor: false, default: []
+    end
+
+    module ClassMethods
+      # Attributes listed as readonly will be used to create a new record but update operations will
+      # ignore these fields.
+      def attr_readonly(*attributes)
+        self._attr_readonly = Set.new(attributes.map(&:to_s)) + (_attr_readonly || [])
+      end
+
+      # Returns an array of all the attributes that have been specified as readonly.
+      def readonly_attributes
+        _attr_readonly
+      end
+    end
+  end
+end