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From: "Hope, Matthew" <Matthew.Hope@capitalone.com>
To: 'Jakarta Commons Users List' <commons-user@jakarta.apache.org>
Subject: RE: Betwixt - CyclicReferenceException
Date: Thu, 18 Sep 2003 13:12:15 -0400
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Are you sure none of these objects contains a reference to it's parent?

Technically (assuming all edges are directed (i.e. one way which is =
what a
simple variable is) this is not cyclic.

Though you may need some betwixt configuration to make sure it treats =
it as
such (I know little about betwixt - sorry)

Matt

-----Original Message-----
From: Michael Watson [mailto:michael.watson@estafet.com]=20
Sent: 18 September 2003 18:01
To: Jakarta Commons Users List
Subject: Re: Betwixt - CyclicReferenceException


Hi Matt,

Thanks for the info - I was heading in the right direction.

It seems that my bean (A) contains the following refs:
A->B->C
A->D->E->C

Is that cyclic? It has these in both scenarios (exception thrown/not
thrown).

Any suggestions why this might only cause me problems in certain =
situations?

Thanks in advance.

Mike

----- Original Message -----=20
From: "Hope, Matthew" <Matthew.Hope@capitalone.com>
To: "'Jakarta Commons Users List'" <commons-user@jakarta.apache.org>
Sent: Thursday, September 18, 2003 5:15 PM
Subject: RE: Betwixt - CyclicReferenceException


A cyclical reference is when a loop exists in your object graph (or =
indeed
any type of graph)

If you have
A- > B
B -> C
C -> A

Then a loop exists and if some algorithm is meant to 'walk' through the
graph and do something at each node (object) then in the situation =
above it
would walk forever going round in a loop.

Graph traversal (walk) algorithms often include mechanisms to avoid =
loops,
either by terminating in a failure state (throw an exception) or by not
traversing an edge to a node already visited.

This implementation is maintaining a set of nodes visited and when a =
node is
revisited it throws an exception.

One area where this can be a pain is if you have a structure

A -> B via variable x
A -> B via variable y

In this case a na=EFve algorithm will call this a revisit - I don't =
know if
betwixt does though

Your two examples would contain one which has no such loop and another =
which
does. Perhaps in one you are reusing an object in two different =
variables?

Matt

-----Original Message-----
From: Michael Watson [mailto:michael.watson@estafet.com]
Sent: 18 September 2003 16:58
To: Jakarta Commons Users List
Subject: Betwixt - CyclicReferenceException


Hi,

I'm having issues with cyclic references and was wondering if anyone =
can
shed some light for me.

I'm calling BeanWriter.write (on a reasonably complex bean) and =
occasionally
getting a cyclicreferenceexception thrown.

I can reproduce the problem easily but the thing that's confusing me is =
that
I can call this method with another instance of the same type of bean =
(with
near identical data) and it doesn't throw an exception.

Can anyone explain exactly what a cyclic reference is, how I might be =
able
to identify what part of the bean is causing it and how I can try and =
avoid
it?

Thanks in advance.

Mike


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