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

Gunnar Morling gunnar at hibernate.org
Mon Dec 16 11:24:04 EST 2013 

2013/12/16 Emmanuel Bernard <emmanuel at hibernate.org>

> 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
>

I'm a bit concerned about this naming approach using verbs. It reads nicely
here, but does it work as well for other cases? E.g. take the write concern
option, @WriteConcern(ACKNOWLEDGED) seems very natural, how would that look
with the verb- based style? I feel with a declarative style using nouns
such as @AssociationStorage we may be on the safer side.

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?
>

I was wondering the same. Not sure about graph DBs, I guess not?


> 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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