Hi,
at the moment i spent some time on a small application using hibernate. I've
did most of the domain's modeling and implementation. Now i have to decide
where to place the database (say hibernate) dependent code.
* Put everything into the domain classes.
* Implement something like a "Home" interface
* Implement some sort of component-like / "Service" interface
Domain Classes with database access
This implementation strategy seems to be the simplest one of all. Database
access is at most implemented as static methods of the domain class. But
unfortunately this establishes a very strong link between the domain classes
and the persistence provider. If i decide to change the persistence provider
for any reason, i have to modify all domain classes.
Implementation of a Home-Interface
This solution seems to keep things moderate simple. Each domain class (e.g.
Actor) owns one associated "home interface" (e.g. ActorHome). Using some
Factory it is possible to obtain a specific implementation (e.g.
ActorHomeHibernateImpl) of that interface. All communication with the
underlying persistence provider is channeled through this interface. The
domain classes will be (almost) free of code dealing with the database
(Lifecycle etc. seems to be still a problem). In this case i have to provide
some abstraction for the persistence services (update(), delete(),
TX-management).
Implementation of Service like structures
This is more or less the same idea like above but with coarser granularity.
In this case i think about interfaces covering note single domain classes
but semantic groups of them. In this way something that smells like a
"component" (with its own lifecycle) could be implemented. Using this
strategy the Service-Interface would behave also as a service provider for
the domain classes. But this design could offer some chances to reimplement
parts of the application using different persistence providers (requires the
domain classes using the Service-Interface if crossing "component" borders).
At this moment i'm not sure wich basic design i should use. Please drop me
some notes about this topic.
* Which is your preffered strategy?
* Why have you choosen your way?
* What are the benefits or the drawbacks?
regards,
Ralf E. Stranzenbach
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