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.

2 files changed, 22 insertions, 12 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 759ac9943f..200b773172 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -61,16 +61,13 @@ module ActiveRecord
           @collation = collation
           @extra     = extra
           super(name, default, cast_type, sql_type, null)
+          assert_valid_default(default)
         end
 
-        def extract_default(default)
-          if blob_or_text_column?
-            if default.blank?
-              null || strict ? nil : ''
-            else
-              raise ArgumentError, "#{type} columns cannot have a default value: #{default.inspect}"
-            end
-          elsif missing_default_forged_as_empty_string?(default)
+        def default
+          @default ||= if blob_or_text_column?
+            null || strict ? nil : ''
+          elsif missing_default_forged_as_empty_string?(@original_default)
             nil
           else
             super
@@ -102,6 +99,12 @@ module ActiveRecord
         def missing_default_forged_as_empty_string?(default)
           type != :string && !null && default == ''
         end
+
+        def assert_valid_default(default)
+          if blob_or_text_column? && default.present?
+            raise ArgumentError, "#{type} columns cannot have a default value: #{default.inspect}"
+          end
+        end
       end
 
       ##
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index 5e4e00bc64..23434df1fe 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -13,7 +13,7 @@ module ActiveRecord
         ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(\.\d+)?\z/
       end
 
-      attr_reader :name, :default, :cast_type, :null, :sql_type, :default_function
+      attr_reader :name, :cast_type, :null, :sql_type, :default_function
 
       delegate :type, :precision, :scale, :limit, :klass, :accessor,
         :text?, :number?, :binary?, :serialized?, :changed?,
@@ -35,7 +35,7 @@ module ActiveRecord
         @cast_type        = cast_type
         @sql_type         = sql_type
         @null             = null
-        @default          = extract_default(default)
+        @original_default = default
         @default_function = nil
       end
 
@@ -51,8 +51,15 @@ module ActiveRecord
         Base.human_attribute_name(@name)
       end
 
-      def extract_default(default)
-        type_cast(default)
+      def default
+        @default ||= type_cast(@original_default)
+      end
+
+      def with_type(type)
+        dup.tap do |clone|
+          clone.instance_variable_set('@default', nil)
+          clone.instance_variable_set('@cast_type', type)
+        end
       end
     end