Domain objects with no dependencys on DAO's

[drc]

Hi,

I have a partitioning question that I'd some feedback on.

Our app uses Spring, Struts and Hibernate, and I'd like to keep our domain model (the Hibernate POJO's) from having any dependencies on our DAO's (that wrap Hibernate). However, consider a domain object that has the business rule that a certain property must be unique. How can this be implemented so that the domain object enforces this business rule, but without having to directly call a DAO in the domain object to enforce it?


many thanks,

drc

[katentim]

Can this logic just be applied in the services layer?

I assume this will be enforced by the DB, so you can have a services method to check the name is available, and also logic to handle data integrity violations.

[drc]

katentim ,

yeah it could be, but I see this as something that ideally belongs in the domain object - which then requires a reference to a DAO to do this, which I dont like.

The other issue is that we are using the same 'Services' object for all CRUD type operations from the UI - which means that I can not check for uniqueness in the services layer.


thanks.

[katentim]

The other issue is that we are using the same 'Services' object for all CRUD type operations from the UI - which means that I can not check for uniqueness in the services layer.

I don't think I follow. Why can't the services layer check for uniqueness? Is this a caching issue?

[drc]

Firstly a definition, our struts actions call into our 'Services' tier. This services tier is generic so it accepts a Collection of domain objects and simply persists them to the db - regardless of what type they are. Each domain object has a method where we put validations, so this method is called prior to persisting it to the db. Given that this Services object is generic, it cant do domain-specific type validations.

The reason why we have such a generic services object is because we have many simple CRUD-type html screens.

I hope this helps.

[katentim]

Given that this Services object is generic, it cant do domain-specific type validations

You could possibly use AOP to apply advice on add methods in the service layer for certain domain object types.

[Colin Yates]

Why can't your validator simply ask the DAO to check the uniqueness?

Sure there is still a window of opportunity to get inconsistent results, but it is a very *very* small one and the DB will throw an exception so it is safe.....

Is it unique within a parent? If so, then why not implement hashCode and equals and just check adding it to the parent's set of children?