[hibernate-dev] [OGM] Precedence of options specified on different levels

[Emmanuel Bernard]

On Mon 2013-12-16 11:06, Gunnar Morling wrote:
> 2013/12/13 Emmanuel Bernard <emmanuel at hibernate.org>
> 
> > So currently in the pull request, we now have the following
> >
> > 1. property > entity > global
> > 2. for each level in 1., programmatic API beats annotation
> >
> > These are simple rules to understand and all it good.
> >
> > Now Gunnar tried to handle class inheritance, ie superclasses and
> > overridden methods.
> > And we do differ in what we consider the natural rules (or what it
> > should be).
> >
> > Here is how I think the rules should be:
> >
> > 1. property > entity > global
> > 2. for each level in 1., subclass > superclass and overridden method >
> > parent method
> > 3. for each level (in 1 and 2), programmatic API beats annotation
> >
> > Here is how Gunnar thinks the rules should be:
> >
> > 1. metadata on a class > metadata on a superclass (whether it is on a
> > property or the class)
> > 2. for each hierarchy level, property > entity > global
> > 3. for each level in 1 and 2, programmatic API beats annotation
> >
> > In more concrete words,
> >
> >     @Option(1)
> >     class A {
> >         @Option(2)
> >         public String getMe() {return null;}
> >     }
> >
> >     @Option(3)
> >     class B extends A {
> >         @Override
> >         public String getMe() {return null;}
> >     }
> >
> > In my world, B.getMe has Options(2).
> > In Gunnar's world, B.getMe() has @Option(3).
> >
> 
> Thanks for the clear explanation and example for the issue.
> 
> 
> > To me, a property level is always more specific than an entity, hence my
> > interpretation. If someone has set a value on a given property, it would
> > be dangerous to be "globally" overridden by a subclass.
> >
> > Thoughts?
> >
> 
> What would be "dangerous" in this case?

Someone has clearly decided that A.getMe should behave in a specific way
and differently than A.getOtherMe. Overriding that via B for all of A's
properties is wrong IMO. Besides, why doesn't it override the settings
for properties that are not overridden?

> 
> I think for the author of B it's helpful to be able to change the defaults
> for the entire class. Also for a reader of B its simpler to grasp the
> applying configuration with my proposal, because the entire "truth" about
> the annotation config can be found in B, you don't have to look into any
> super-classes. So to me, that's more along the lines of the principle of
> least surprise.
> 

If you consider that the truth should be in the most specific entity, I think
you should also consider that inheriting the settings from the
superclass is against that principle and that inheritance should not be
involved.

Emmanuel