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

Emmanuel Bernard emmanuel at hibernate.org
Mon Dec 16 07:34:22 EST 2013 

I think in this specific case it does make sense to have a global
setting and a specific one for the additional mongodb if we rephrase
then like think

@StoreAssociations(IN_ENTITY, AS_DOCUMENT) (should it be AS_SEPARATE_DOCUMENT or AS_SEPARATE_ENTRY)
@StoreAssociationsInSeparateCollection //mongo specific

BTW is that a generic setting or something dedicated to document
datastore.
Does it work for k/v? I think it does.
Does it work for GraphDBs?

On Mon 2013-12-16 10:46, Gunnar Morling wrote:
> On a related note, Emmanuel raised the question whether to use the same
> option types for different data stores or not, i.e. should we use the same
> @AssociationStorage annotation and enum for MongoDB and CouchDB?
> 
> Currently there are the following strategies:
> 
> * MongoDB: GLOBAL_COLLECTION, COLLECTION, IN_ENTITY
> * CouchDB: ASSOCIATION_DOCUMENT, IN_ENTITY
> 
> So we have IN_ENTITY in both, but the other strategies don't directly map
> to each other. CouchDB doesn't have a notion of "collections", so
> ASSOCIATION_DOCUMENT is most similar to GLOBAL_COLLECTION from MongoDB
> (considering the one and only document heap as the "global collection",
> whereas that maps to a specific "associations" collection for the MongoDB
> backend).
> 
> So in a shared enum we might have values like these: IN_ENTITY,
> ASSOCIATION_DOCUMENT, ASSOCIATION_DOCUMENT_ORGANIZED_BY_ASSOCIATION.
> 
> The latter would only be supported on MongoDB and raise an exception when
> used with CouchDB. To make the options usable for other document stores as
> well, I think we should avoid datastore specific terms such as "collection"
> in the enum values.
> 
> As an alternative we could have only IN_ENTITY and ASSOCIATION_DOCUMENT on
> the shared enum (It seems quite save to assume that this makes sense in
> every document store). The MongoDB dialect could then provide an additional
> option which allows to specify the store-specific collection vs. global
> collection aspect:
> 
>     @AssociationStorage(ASSOCIATION_DOCUMENT) //shared annotation/enum
>     @AssociationDocumentStorage(GLOBAL_COLLECTION) //mongo-specific
> annotation/enum
> 
> I slightly prefer that last approach because it doesn't expose any specific
> things on the shared contracts, although increasing the complexity a bit by
> having two options for MongoDB.
> 
> --Gunnar
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 2013/12/16 Emmanuel Bernard <emmanuel at hibernate.org>
> 
> > 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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> >

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