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From Michael Dick <michael.d.d...@gmail.com>
Subject Re: Multibyte characters on SQL Server and Sybase
Date Mon, 11 Jan 2010 15:24:44 GMT
Hi Craig,

That sounds reasonable for this specific use case. I'm a little leery of
doing too much validation of the columnDefinition attribute, though. It just
seems pretty easy for us to get it wrong (ie converting VARCHAR to LVARCHAR
based on the column length, or some other optimization).

What about adding a variable to DBDictionary along the lines of
"preferNLSVarChar", and then we'll try to use the database's specific
NVARCHAR equivalent?

Marc, presumably you have different persistence unit definitions for each
database. If that's the case then you could use a different xml-mapping-file
and set the columnDefinitions to the database specific type in the
xml-mapping-file.

Or even more hacky, you could just override the VARCHAR type in the
DBDictionary. Ie add this property to persistence.xml :
<property name="openjpa.jdbc.DBDictionary(varCharTypeName=NVARCHAR)"/>

Either way the application will have to know the proper type, but at least
you can make some progress.

-mike

On Fri, Jan 8, 2010 at 1:34 PM, Craig L Russell <Craig.Russell@sun.com>wrote:

>
> On Jan 8, 2010, at 11:00 AM, Marc.Boudreau wrote:
>
>
>> No, the problem is that code can be run on a variety of database platforms
>> like DB2, SQL Server, Oracle, etc...
>> So if I use @Column(columnDefinition="NVARCHAR(256)"), it will only work
>> on
>> SQL Server and Sybase, because the other database platforms don't
>> recognize
>> the NVARCHAR type.
>>
>
> I see. How about having the DataDictionary process the columnDefinition in
> a database-specific way? IIRC, all of the databases support national use
> character set columns but in their own way.
>
> The columnDefinition is not further standardized in the specification so we
> can do anything we want to with it.
>
> We could analyze the columnDefinition and look for the ANSI standard
> strings NCHAR(n) and NVARCHAR(n) and translate these into the
> database-specific type.
>
> Craig
>
>
>>
>> Craig L Russell wrote:
>>
>>>
>>> Hi,
>>>
>>> On Jan 8, 2010, at 7:53 AM, Marc Boudreau wrote:
>>>
>>>
>>>>
>>>> Currently, OpenJPA maps String fields to VARCHAR on SQLServer and
>>>> Sybase.
>>>> There doesn't appear to be a way to cause a String field to be
>>>> mapped to
>>>> NVARCHAR other than by using the @Column annotation and settings its
>>>> columnDefinition to "NVARCHAR".
>>>>
>>>
>>> What is the objection to using this technique on the columns that you
>>> want to hold national use characters? It seems this use case is
>>> exactly suited to this feature.
>>>
>>>  At the same time, blindly using NVARCHAR
>>>> for all String fields is too costly in terms of storage space on the
>>>> database.  It ends up limiting the maximum size of the column (less
>>>> characters can fit because more bytes are used to store them).
>>>>
>>>> Unfortunately, the applications we write are required to be database
>>>> neutral because we support multiple vendors.
>>>>
>>>> I'd like to start a discussion on this matter.  Here are a couple of
>>>> points
>>>> to lead us off...
>>>>  What's the severity of this missing functionality?
>>>>  Could an OpenJPA specific annotation be introduced to allow the
>>>> mapping
>>>>  tool to use NVARCHAR instead of VARCHAR?.
>>>>
>>>
>>> Is the problem that the OpenJPA mapping tool doesn't support the
>>> standard columnDefinition annotation in the way you want it to?
>>>
>>> Craig
>>>
>>>
>>>>
>>>>
>>>> Marc Boudreau
>>>> Software Developer
>>>> IBM Cognos Content Manager
>>>> marc.boudreau@ca.ibm.com
>>>> Phone: 613-356-6412
>>>>
>>>
>>> Craig L Russell
>>> Architect, Sun Java Enterprise System http://db.apache.org/jdo
>>> 408 276-5638 mailto:Craig.Russell@sun.com
>>> P.S. A good JDO? O, Gasp!
>>>
>>>
>>>
>>>
>> --
>> View this message in context:
>> http://n2.nabble.com/Multibyte-characters-on-SQL-Server-and-Sybase-tp4274154p4274294.html
>> Sent from the OpenJPA Users mailing list archive at Nabble.com.
>>
>
> Craig L Russell
> Architect, Sun Java Enterprise System http://db.apache.org/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!
>
>

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