Beans, DAOs, Services, applications

Im working on a Utility that does standard CRUD stuff. My brain got a little confused, again, in the area of relationships between services, beans and DAOs. Specifically, i could not decide the best way to implement the relationships between the three. In a SOA, we use the Service object as the laison between the application and the domain objects. Does the service also keep the responsibility of creating a persistence bean for a certain object? I think so, i added the instantiation of the resource persistence bean into the init() of the service. Now the service init() function instantiates DOA, Gateway and bean objects. I am using the variables scope in front of each and have tested the threading, which should not be a problem, since each user who instantiates their own service object gets there own copy of each of the other objects.



In my service, I have a set bean method, that updates the "empty" bean object, by passing a objectID into the set bean method - which then goes to the DAO, since thats the object that should have the SQL or whatever DB code you are using. The bean itself should not know about the database that is being used to get its data so it can do its job of persisting. So, the service calls a getRecord method in the DAO, the DAO sends back a 1 record query to the service. Teh service checks to be sure it has a valid result and then passes the query result to the set bean method in the bean itself.



This seems to make sense - following these good OO practices.

• Service creates objects needed to do the work requested by application
  
• Service asks the DAO to get a single record, passing in objectID
  
• DAO returns a single record
  
• Service ensure the record returned is valid (this could be done in DAO too)
  
• Service then calls the set bean method in the bean itself, passing in the record to update
  

In conclusion:

• The DOA does not know about the beans
• The beans do not know about the database
• The service knows about beans and DAOs and Gateways and other services.