Question

It occurs to me that state control in languages like C# is not well supported.

By this, I mean, it is left upto the programmer to manage the state of in-memory objects. A common use-case is that instance variables in the domain-model are copies of information residing in persistent storage (i.e. the database). Clearly this violates the single point of authority principle, and "synchronisation" has to be managed by the developer.

I envisage a system where instead of instance variables, we have simple public access/mutator methods marked with attributes that link them to the database, and where reads and writes are mediated by a framework that decides whether to hit the database. Does such a system exist?

Am I completely missing the point, or is there some truth to this idea?

Answer 1

If i understand correctly what you want: Any OR-Mapper with Lazy Loading is working this way. For example i use Genome and there every entity is a pure proxy and you have quite much influence to tell the OR-Mapper how to cache the fields.

Answer 2

Actually there s the concept of data prevalence (as implemented by prevayler in Java) where the in-memory objects are the single point of authority (SPA) for the data.

Also, some object databases (as db4o) blur lines a bit between the object representation and the "store" representation.

On the other hand, by bringing the SPA for the data inside the application, you need to handle transactions and/or data persistence by yourself. There is some work done on transactional memory systems such as JVSTM (currently in use by the information system of my old college) but it s not in widespread use.

On the other hand, if the data lives in a database, you can just commit the data when everything is good (or use the support for transactions built in the database) and be sure that data isn t corrupted or lost. You trade in the SPA principle for better data reliability and transactions (and other advantages of using a separate data store)

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