code: @Override
      public <T> T readInstance(DatastoreType datastoreType) {
          return getInstance(datastoreType, TransactionalCache.Mode.READ);
      }
docs: Return the proxy instance which corresponds to the given datastore type for
  reading.
  
  @param datastoreType
  The datastore type.
  @param <T>
  The instance type.
  @return The instance.