JSON is still an adapter specific type.

Several changes were made in #21110 which I am strongly opposed to.
(this is what I get for going on vacation. :trollface:) No type should
be introduced into the generic `ActiveRecord::Type` namespace, and
*certainly* should not be registered into the registry unconstrained
unless it is supported by *all* adapters (which basically means that it
was specified in the ANSI SQL standard).

I do not think `# :nodoc:` ing the type is sufficient, as it still makes
the code of Rails itself very unclear as to what the role of that class
is. While I would argue that this shouldn't even be a super class, and
that MySql and PG's JSON types are only superficially duplicated (they
might look the same but will change for different reasons in the
future).

However, I don't feel strongly enough about it as a point of contention
(and the biggest cost of harming the blameability has already occured),
so I simply moved the superclass into a namespace where its role is
absolutely clear.

After this change, `attribute :foo, :json` will once again work with
MySQL and PG, but not with Sqlite3 or any third party adapters.

Unresolved questions
--------------------

The types that and adapter publishes (at least those are unique to that
adapter, and not adding additional behavior like `MysqlString` should
probably be part of the adapter's public API. Should we standardize the
namespace for these, and document them?

1 files changed, 33 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/type/internal/abstract_json.rb b/activerecord/lib/active_record/type/internal/abstract_json.rb
new file mode 100644
index 0000000000..963a8245d0
--- /dev/null
+++ b/activerecord/lib/active_record/type/internal/abstract_json.rb
@@ -0,0 +1,33 @@
+module ActiveRecord
+  module Type
+    module Internal # :nodoc:
+      class AbstractJson < Type::Value # :nodoc:
+        include Type::Helpers::Mutable
+
+        def type
+          :json
+        end
+
+        def deserialize(value)
+          if value.is_a?(::String)
+            ::ActiveSupport::JSON.decode(value) rescue nil
+          else
+            value
+          end
+        end
+
+        def serialize(value)
+          if value.is_a?(::Array) || value.is_a?(::Hash)
+            ::ActiveSupport::JSON.encode(value)
+          else
+            value
+          end
+        end
+
+        def accessor
+          ActiveRecord::Store::StringKeyedHashAccessor
+        end
+      end
+    end
+  end
+end