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

[Emmanuel Bernard]

Only the CouchDB provider in the PR so far. But the idea is to move all
to that model.

On Fri 2013-12-13 16:35, Guillaume SCHEIBEL wrote:
> Hi guys,
> 
> That sounds nice. Are association storage strategies already using this new
> feature ?
> 
> 
> Guillaume
> 
> 
> 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).
> >
> > 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?
> >
> > Emmanuel
> >
> > On Tue 2013-12-03 10:48, Gunnar Morling wrote:
> > > Hi,
> > >
> > > In the context of embedded associations for CouchDB [1], I'm working on
> > > support for configuring the association storage mode using our new option
> > > system [2]. I can see the following "axes" of configuration here:
> > >
> > > * via annotation
> > >   - on an association property
> > >   - on a type
> > > * via the option API
> > >   - on an association property
> > >   - on a type
> > >   - on the global level
> > > * via a configuration property as given via OgmConfiguration,
> > > persistence.xml etc.
> > > * on super-types
> > >   - via annotations or API
> > >   - on the property or entity level
> > >
> > > I'm looking now for a sensible and comprehensible algorithm for taking
> > > these sources of configuration into account and determining the effective
> > > setting for a given association. This could be one way:
> > >
> > > 1) check API
> > >   a) look for a setting given via the programmatic API for the given
> > > property
> > >   b) if the property is not configured, look for a setting given for the
> > > entity
> > >   c) if the entity itself is not configured, repeat a) and b) iteratively
> > > on super-types if present
> > >   d) if no type from the hierarchy is configured look for the global
> > setting
> > >
> > > 2) check annotations
> > >   if no configuration could be found in 1), do the same for annotations,
> > > i.e.
> > >   a) look for configuration on the given property
> > >   b) look for configuration on the given entity
> > >   c) repeat a) and b) iteratively on super-types if present
> > >
> > > 3) take default value given via OgmConfiguration/persistence.xml etc.
> > >
> > > This algorithm ensures that:
> > > * API configuration always takes precedence over annotation
> > configuration;
> > > e.g. if a super-type is configured via the API or the setting is given on
> > > the API global level, any annotations are ignored
> > > * "More local" configuration takes precedence; i.e. a type's own
> > > configuration wins over configuration from super-types, property-level
> > > configuration wins over entity-level configuration
> > >
> > > Note that any setting given via OgmConfiguration/persistence.xml would be
> > > handled as last fallback option, i.e. any configuration given via
> > > annotations or the API would take precedence over that. I first didn't
> > like
> > > that but I came to think it makes sense, if the property name conveys
> > that
> > > semantics, e.g. "defaultAssociationStorageMode".
> > >
> > > Any other thoughts or alternative approaches around this?
> > >
> > > Thanks,
> > >
> > > --Gunnar
> > >
> > > [1] https://hibernate.atlassian.net/browse/OGM-389
> > > [1] https://hibernate.atlassian.net/browse/OGM-208
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