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From Andrus Adamchik <and...@objectstyle.org>
Subject Re: Parent/Child Insert ordering (was: Caching problem?)
Date Sun, 21 May 2006 17:24:12 GMT
Cayenne handles correct ordering of operations automatically, based  
on dependencies derived from relationships.The algorithm has a few  
limitations though. It can't handle cycles (when Entity A depends on  
Entity B, but also Entity B depends on Entity A). This probably also  
includes entities that have relationships to the same entity (I  
assume this is the case the original post was referring to).

There are few solutions:

1. (a workaround, rather than a solution) Do commit in two steps.
2. Define FK constraints in question as DEFERRABLE and INITIALLY  
DEFERRED (supported by Postgres 8.*)
3. Set a custom org.objectstyle.cayenne.map.EntitySorter on the  
DataNode.

Andrus


On May 20, 2006, at 3:00 AM, Marcin Skladaniec wrote:

> Hm. Strange. I do really complex commits, sometimes 7 or more  
> related records (I mean 7 levels of relationship, not seven  
> entities), related by many-to-many many-to-one relationships and  
> never get those problems. And it doesn't matter if the records are  
> new or old. Could you describe how you are creating objects and how  
> do you commit them ?
>
> Regards
> Marcin
>
> On 20/05/2006, at 4:31 PM, Tomi NA wrote:
>
>> On 5/20/06, Jeff de Vries <jdevries@pfrog.com> wrote:
>>> I don't know if it is related or not, but I've also had problems  
>>> in the
>>> past when I try to create a new parent and several child objects  
>>> related
>>> to that parent all at once and then try to commit.  The problem  
>>> looks
>>> like Cayenne is INSERTing the child records into the database first,
>>> before the parent record, and the database complains that the  
>>> children
>>> have an invalid foreign key (and, yes, I have the ON UPDATE and ON
>>> DELETE rules for the foreign key set to DO NOTHING and I still  
>>> get the
>>> error from PostgreSQL).  To get around it I just committed the  
>>> parent
>>> first, then committed all the children.
>>
>> I had the same problem, IIRC: I was very surprised that cayenne
>> couldn't handle such a commit, although truth be told, I can't  
>> imagine
>> everything that's going on under the hood of the operation that would
>> make implementing this feature difficult.
>> I would certainly love to see this fixed (if at all possible) as I
>> wasn't to happy to have to commit in the middle of what had to be an
>> atomic transaction. It'd also make the framework a lot more flexible,
>> e.g. enabling the user to have long inter-commit sessions with  
>> complex
>> data updates, if the user so desires.
>>
>> t.n.a.
>
>


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