From #dm-middleware on slack:

I'd like to get Datastores using the new schema stuff I added recently (TableSpec/FieldSpec) for anything they want to keep in the registry database, and I want to stop using a dict interface, as it's hard to map _setitem_ to insert and update, especially for bulk operations.  I'm thinking of:

• Removing DatabaseDict and DatabaseDictRecordBase entirely.
• Add abstract methods to StoredDatastoreItemInfo to translate to/from dictionaries that correspond to records to be saved.
• Moving the logic for inserting and retrieving StoredDatastoreItemInfo from the database directly into GenericDatastoreBase.  That would probably be _insert_info and _fetch_info methods that replace _info_to_record and _record_to_info.
• Overriding _insert_info and _fetch_info in InMemoryDatastore to save into a dict instead of letting GenericDatastoreBase's implementations write to the database.