[OJB-developers] [Fwd: Re: DescriptorRepository and ReverseDb]

[Thomas M. <tho...@ho...>]

-------- Original Message --------
Subject: Re: DescriptorRepository and ReverseDb
Date: Sat, 15 Jun 2002 23:14:05 +0200
From: Thomas Mahler <tho...@ho...>
To: Florian Bruckner <bf...@fl...>
CC: obj...@li...
References: <LLB...@fl...>

Hi Florian,

Florian Bruckner wrote:
 > Hi!
 >
 > Having found some spare time again I'm looking into integrating
 > DescriptorRepository and friends into ReverseDb. Unfortunately I'm having
 > some problems with the design.
 >
 > My first problem is that DescriptorRepository requires the classes 
already
 > to be there in bytecode. While this is perfectly ok with the normal 
use of
 > DescriptorRepository this is a major problem for ReverseDb, simply 
because
 > at that stage you usually do not have the classes.

Right. I anticipated your problems already when I had a short look at
your reversedb code some time ago.

 > To be able to use
 > DescriptorRepository with ReverseDb there must be a possibility to load a
 > repository and create ClassDescriptor objects without the necessary 
classes.

I agree. We really need this feature!

 > I have not looked at the implementation of these classes yet, but I frear
 > that this might require a major redesign of these classes.

Some work is needed, but I don't think it's going to be a major redesign.
It's not really required to load the persistent classes etc.
immediately. I think it can be delayed until clients try to access them.

 > On the other hand
 > it would be nice if we could use the DescriptorRepository framework in
 > ReverseDb (at least in a useful way).
 >

I agree. I want to have *all* mapping metadata in the
DescriptorRepository and nowhere else.

 > The second problem is the singleton design of DescriptorRepository.

We have to get rid of this too!

 > While it
 > is possible to create new instances of the class, some other classes 
in that
 > framework rely on the fact that it is a singleton (e.g. ClassDescriptor
 > accesses DescriptorRepository by its getInstace() method). In a GUI
 > application (at least in a GUI application I'd like to use) you should be
 > able to open multiple windows with OJB repositories, maybe because 
you want
 > to compare the content or maybe you want to copy class descriptors or 
other
 > elements from one repository to the other.
 >

I agree. There are other places (e.g. PersistenceBrokerFactory) that are
already prepared to work with multiple repository instances.

 > While the second problem could be worked around by simply allowing 
only one
 > instance of a repository-editor-window to be opened, the first issue 
would
 > make it necessary to create a "functional copy" of DescriptorRepository,
 > which I'd like to avoid if possible.
 >
 > Any ideas or comments how we could proceed here or do you think these
 > requirements are so out of scope for OJB that it is not feasable to
 > implement them?
 >

We should work on the necessary refactorings as mentioned above! We want
to have several metadata tools that can't live with the current
restrictions!

 > best regards,
 > Florian
 >
 > PS: I'd like to check-in a completely redesigned prototype of 
reversedb when
 > the repository has been migrated to jakarta if nobody objects. I 
think the
 > design is more flexible now and could serve as the basis for a complete
 > reverse-engineering, repository-editing tool.
 >

no objections. Just go ahead!

cheers,

Thomas