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From "Jukka Zitting (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OAK-33) Values in oak-core
Date Wed, 21 Mar 2012 18:25:41 GMT

    [ https://issues.apache.org/jira/browse/OAK-33?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13234805#comment-13234805
] 

Jukka Zitting commented on OAK-33:
----------------------------------

In revision 1303477 I dropped the {{getDecimal()}} method from the {{Scalar}} interface until
we decide which range of value types to support at this level of abstraction. I think we have
two main alternatives:

* Support only those types that can be directly expressed on the MicroKernel level, essentially
just JSON types and binaries. Note that _numbers_ are a bit vaguely defined in JSON (and JavaScript
in general), so {{getDecimal()}} might actually be better than {{getLong()}} and {{getDouble()}}.
Ultimately we need to figure out how the MicroKernel expects to store numbers and use that
as the basis of our abstraction.
* Support the full set of JCR types. Things like names, paths, and references would still
be opaque at this level (we wouldn't have namespace mappings or dereferencing methods), but
such values would still be explicitly typed.

My intuition is to prefer the first option, but I don't have a stronger opinion on this.
                
> Values in oak-core
> ------------------
>
>                 Key: OAK-33
>                 URL: https://issues.apache.org/jira/browse/OAK-33
>             Project: Jackrabbit Oak
>          Issue Type: New Feature
>          Components: core
>            Reporter: Thomas Mueller
>
> There is no JCR API in oak-core, but we still need to deal with values and data types.
We have multiple options, I can think of:
> (A) String everywhere, as in oak-mk
> (B) Use javax.jcr.Value
> (C) An immutable "Value" class (but doesn't need to be called "Value")
> There are multiple problems with (A), for example compile time safety, and I fear the
code would get unnecessarily complex, not as efficient as it could get (specially when dealing
with numbers), memory usage would be higher.
> I think we said (B) isn't an option because we don't want to use the JCR API in oak-core
(see also OAK-16).
> As for (C), I have a first prototype, mainly because I needed it to be able to migrate
the query feature to oak-core. The prototype is in
>   org.apache.jackrabbit.oak.query.ValueFactory
>   org.apache.jackrabbit.oak.query.Value
>   org.apache.jackrabbit.oak.query.PropertyType
> It's very similar to javax.jcr (even the property types are the same), but the values
are immutable. They currently implement Comparable<Value>, but that's also open for
discussion. One sub-problem is binaries: should they contain a reference to the MicroKernel
instance, or some other "storage backend" (possibly a temp file backend)?
> Concrete suggestions (and patches) are welcome.

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