Don't query the database schema when calling `serialize`

We need to decorate the types lazily. This is extracted to a separate
API, as there are other refactorings that will be able to make use of
it, and to allow unit testing the finer points more granularly.

1 files changed, 34 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/attribute_decorators.rb b/activerecord/lib/active_record/attribute_decorators.rb
new file mode 100644
index 0000000000..596161f81d
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_decorators.rb
@@ -0,0 +1,34 @@
+module ActiveRecord
+  module AttributeDecorators # :nodoc:
+    extend ActiveSupport::Concern
+
+    included do
+      class_attribute :attribute_type_decorations, instance_accessor: false # :internal:
+      self.attribute_type_decorations = Hash.new({})
+    end
+
+    module ClassMethods
+      def decorate_attribute_type(column_name, decorator_name, &block)
+        clear_caches_calculated_from_columns
+        column_name = column_name.to_s
+
+        # Create new hashes so we don't modify parent classes
+        decorations_for_column = attribute_type_decorations[column_name]
+        new_decorations = decorations_for_column.merge(decorator_name.to_s => block)
+        self.attribute_type_decorations = attribute_type_decorations.merge(column_name => new_decorations)
+      end
+
+      private
+
+      def add_user_provided_columns(*)
+        super.map do |column|
+          decorations = attribute_type_decorations[column.name].values
+          decorated_type = decorations.inject(column.cast_type) do |type, block|
+            block.call(type)
+          end
+          column.with_type(decorated_type)
+        end
+      end
+    end
+  end
+end