Question

I am implementing a simple application for expenses reporting.The application will use GAE. In my application I have several entities (Classes) like Year, Month,Day, Expenses, Account and so on. The picture is as follow: a user can create an Account, then start to declare expenses with a simple form. The expenses are stored in GAE Datasotre. Every Year has Months, every month has Days and every day has a declared Expenses.the problem is that i don’t know how to arrange theses entities in the non-relational database of GAE. I read several tutorial and articles from Google Developers website, but still don’t understand the concept of Parent/child relationship and groups of entities. Anyone can help with some tutorial,video, articles or books on how to design the relationship and store your entities in a Non-relations database like GAE Data store. thanks in advance. I forget to mention that I would like to use GAE low-level data store.

Answer 1

If you are using java, I would suggest using objectify. It’s just so much easier than JPA, for me at least.

You are paying by the read and write, so if for instance you can fit all of the data for a month in 1mb, then I would not have a separate entity for day. Anyway, I don’t understand your requirements like why year has to be an entity and can just be a property that you filter by. I would actually think about just having a Day entity with Year, and Month properties to filter by.

http://code.google.com/p/objectify-appengine/wiki/IntroductionToObjectify#Relationships