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From Daniel John Debrunner <...@debrunners.com>
Subject Re: Why are classpath databases always read-only ?
Date Thu, 08 Dec 2005 16:58:59 GMT
Thomas Dudziak wrote:

> On 12/8/05, Daniel John Debrunner <djd@debrunners.com> wrote:
> 
>>Thomas Dudziak wrote:
>>
>>
>>>the manual says
>>>(http://db.apache.org/derby/docs/10.1/devguide/rdevdvlp38881.html):
>>>
>>>"classpath   Databases are treated as read-only databases, and all
>>>databaseNames must begin with at least a slash, because you specify
>>>them "relative" to the classpath directory."
>>>
>>>Now I wonder why that is so ? Is there a particular reason to treat
>>>these always as read-only ? If the classpath points to a local
>>>directory (as opposed to, say, a jar), Derby could easily resolve this
>>>to a real path and work with this.
>>
>>Only because no-one has asked for this feature and maybe at the time I
>>didn't realise you could get to the real path from the resource. When
>>this feature was added Cloudscape was running on JDK 1.1 where the
>>getURL method was not available.
> 
> 
> Would you consider adding it ? I think that is would be really useful
> because it would decouple the app from where it runs (without having
> to run Derby in server mode).

If the 'you' means me, then I don't have the time or the itch to add it.
I'm willing to provide guidance on how to do it.

If the 'you' means the Derby community, then if someone provided this
functionality I can't see it being rejected.

>>>This would allow web applications to be created with an initial,
>>>embedded Derby database without having to hard-code the absolute
>>>database path (no assumption can be made as to where the current
>>>working directory is when running in a servlet container, so the path
>>>must be absolute).
>>
>>Also, you can package a read-only database in a jar file and archive
>>that in the web-application archive, war or ear file. Then one can
>>distribute read-only data with web-applications and access that data
>>without ever unpacking the war/ear file and not knowing its location on
>>disk.
> 
> 
> Sure, but that is exactly the point: the database is read-only. If I
> want to have an embedded database (e.g. co-located to the web app,
> say, in WEB-INF/classes/derbydb) then I have to use a jdbc directory
> url with an absoulte path which kind of defeats the concept of WARs.
> Or I have to determine the JDBC url at runtime as a workaround, but
> that IMHO is ugly.

Maybe you could explain how this would work? Are you assuming that the
war/ear file is always unpacked into the local file system? Is that
guaranteed for a J2EE server?

Dan.


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