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

[Gunnar Morling]

Thanks, Davide.

2013/12/3 Davide D'Alto <davide at hibernate.org>

> It looks good to me.
>

Ok.

> I first didn't like that but I came to think it makes sense, if the
> property name conveys that semantics, e.g. "defaultAssociationStorageMode".
>
> I don't think it's necessary to use the prefix "default". For me it is
> just a setting that it is overridden by something else in some situations,
> the same as an annotation is declared at the same time on the class and on
> an attribute.
>

>From what I can say it's reasonable for a user to expect that properties
given via persistence.xml or similar actually do apply and are not
overridden by code or annotations.

Take the MongoDB "host" as example, here we have an internal constant with
a default but the user can set "hibernate.ogm.mongodb.host" and this
setting applies. That's different from the proposed algorithm where the
property really would only be used as fallback if not configuration is
given by means of annotations or API.

Thus I think it makes sense to make this semantics transparent via the
"default..." prefix in the property name.


>
> Davide
>
>
>
> On Tue, Dec 3, 2013 at 9:48 AM, Gunnar Morling <gunnar at hibernate.org>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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>
>