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From Pinaki Poddar <ppod...@apache.org>
Subject Re: FieldMetaData questions
Date Tue, 10 Mar 2009 16:10:34 GMT

Hi,
 > such that I could tag a field with a custom-defined property-value pair
and retrieve it? 

  Yes you can. At meta-level, you can mark a Field carrying implementation
specific data. See FieldMetaData.usesImplData();
  At an instance level every element can be attached with a 'user object'
which is opaque  to OpenJPA runtime.

> For example, in our current legacy code, we have the idea of a "hidden"
> property.  I would like to be 
> able to retrieve this when looping through the fields in order to
> correctly transform the data to
> our existing legacy structures.

  The other option (which is simpler) is to use Externalizer support that
annotates a field with a pair of conversion functions to translate between
in-memory and data store representation.
  A more involved approach in to write custom value handlers. 
  
  Both of them (externalizer and custom value) are adequately documented in
OpenJPA documentation. 

  Regards --

Pinaki


Heather Sterling wrote:
> 
> 
> 
> Hi,
> 
> I was wondering how to retrieve the possible enum values from a
> FieldMetaData structure.
> 
> I also wanted to know if there's a way to get other information, such as
> the length of a field. (specified with @Column annotation).  I assume
> there
> is, but I could not find it.
> 
> Lastly, is there a way to extend the metadata, such that I could tag a
> field with a custom-defined property-value pair and retrieve it?  I saw
> that there are some extension APIs on FieldMetaData, but I'm not sure what
> the purpose of those are.  For example, in our current legacy code, we
> have
> the idea of a "hidden" property.  I would like to be able to retrieve this
> when looping through the fields in order to correctly transform the data
> to
> our existing legacy structures.
> 
> Thanks,
> 
> Heather Sterling
> Systems Management Development
> Phone:  919-254-7163 T/L: 444-7163
> Cell: 919-423-3143
> Email: hsterl@us.ibm.com
> 

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