using objectify how to get a subset of properties for an object

I have a large object that I store using objectify. I need a lis开发者_StackOverflowt of those objects with only subset of the properties populated. How can this be done?

App Engine stores and retrieves entities as encoded Protocol Buffers. There's no way for the underlying infrastructure to store, update, or retrieve only part of an entity, so there's no point having a library that does this - hence Objectify, like other libraries, don't. If you regularly need to access only part of an entity, split those fields into a separate entity.

It's not a good idea to split an entity in two in a noSql database: when you need to read a list of entries, you would be obliged to do n requests to get the second part of the list (n x m if your data is split in more entities). This is naturally due to the fact that there is no possible join in noSql databases.

What could be done is to "cache": duplicate the needed subset in another entity to get the most of performance. It has the disadvantage of being obliged to write twice on a persist of the main entity (if a field of the subset was changed).

What I usually do is write a /** OPTIMIZE xxxx */ comment on the class that needs to read a subset and get back to it when I need more performance.