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

[Emmanuel Bernard]

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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