pg, keep `hstore` and `json` attributes as `Hash` in @attributes.

The solution presented in this patch is not efficient. We should replace it
in the near future. The following needs to be worked out:
  * Is `@attributes` storing the Ruby or SQL representation?
  * `cacheable_column?` is broken but `hstore` and `json` rely on that behavior

Refs #15369.

/cc @sgrif @rafaelfranca

2 files changed, 14 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb
index 98f369a7f8..bf680b6624 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb
@@ -8,7 +8,13 @@ module ActiveRecord
           end
 
           def type_cast_for_write(value)
-            ConnectionAdapters::PostgreSQLColumn.hstore_to_string value
+            # roundtrip to ensure uniform uniform types
+            # TODO: This is not an efficient solution.
+            cast_value(type_cast_for_database(value))
+          end
+
+          def type_cast_for_database(value)
+            ConnectionAdapters::PostgreSQLColumn.hstore_to_string(value)
           end
 
           def cast_value(value)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
index 42bf5656f4..42a5110ffd 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
@@ -8,7 +8,13 @@ module ActiveRecord
           end
 
           def type_cast_for_write(value)
-            ConnectionAdapters::PostgreSQLColumn.json_to_string value
+            # roundtrip to ensure uniform uniform types
+            # TODO: This is not an efficient solution.
+            cast_value(type_cast_for_database(value))
+          end
+
+          def type_cast_for_database(value)
+            ConnectionAdapters::PostgreSQLColumn.json_to_string(value)
           end
 
           def cast_value(value)