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From Justin Patterson <jus...@pattersonhouse.net>
Subject Re: Question about delete-connected restrictions
Date Thu, 02 Feb 2006 02:14:55 GMT
It looks like that is, indeed, the problem.  I just commented out that 
DDL-time check and now it's working fine.  I realize that I have nothing 
to cover me at run-time, but the situation is not going to come up in my 
app.  I'll just upgrade when the fix makes it in officially.

Thanks!

-Justin

Satheesh Bandaram wrote:

> Hi Justin,
>
> You may be hitting DERBY-338 
> <http://issues.apache.org/jira/browse/DERBY-338>. I think the problem 
> there is Derby tries to catch possible conflict in cascade delete 
> actions at DDL time, when a runtime checking is what is needed. In 
> your case, you said, you don't expect a conflict at run-time.
>
> There is a partial patch pending for DERBY-338 for long time now. It 
> is probably out of sync with the code. Do you think that could be the 
> problem you are seeing? Is there anyway you can define your DDL 
> without "conflicting actions" as Derby seems to think? Derby also has 
> triggers, if you could use that for part of your schema.
>
> Satheesh
>
> Justin Patterson wrote:
>
>> Hey Derby Users,
>>
>> I'm designing an application to keep up with my music collection.  
>> It's currently running fine on Hibernate/One$DB until I execute 20k 
>> or so transactions.  Then, the JVM runs out of memory.  After 
>> profiling it, I determined that the leaks are related to One$DB and 
>> that's just the final straw for me.  I submitted some questions to 
>> the One$DB forums, but they're not very active and there doesn't seem 
>> to be a new version forthcoming.  So, I'm shopping aroiund for a 
>> better embedded RDBMS and I've heard great things about Derby.
>>
>> After porting my schema over, I ran into something that's peculiar 
>> (to me, anyway) and I'd appreciate any advice that you can give.  My 
>> apologies if this is not Derby-specific, but I didn't have any 
>> problems doing this in my schema with either MySQL or One$DB.
>>
>> Here are the important snippets from my DDL script (I snipped the 
>> irrelevant columns and tables):
>>
>> CREATE TABLE playable (
>>  id INTEGER GENERATED ALWAYS AS IDENTITY,
>>  CONSTRAINT pk_playable_id PRIMARY KEY (id)
>> );
>>
>> CREATE TABLE track (
>>  id INTEGER,
>>  CONSTRAINT pk_track_id PRIMARY KEY (id),
>>  CONSTRAINT fk_track_id FOREIGN KEY (id) REFERENCES playable_t(id) ON 
>> DELETE CASCADE
>> );
>>
>> CREATE TABLE mediafile (
>>  id INTEGER,
>>  trackid INTEGER,
>>  CONSTRAINT pk_mediafile_id PRIMARY KEY (id),
>>  CONSTRAINT fk_mediafile_id FOREIGN KEY (id) REFERENCES 
>> playable_t(id) ON DELETE CASCADE,
>>  CONSTRAINT fk_mediafile_trackid FOREIGN KEY (trackid) REFERENCES 
>> track_t(id) ON DELETE SET NULL
>> );
>>
>> When I run that, I get:
>>
>> ERROR 42915: Foreign  Key 'FK_MEDIAFILE_TRACKID' is invalid because 
>> 'the delete rule of foreign key must be CASCADE. (The relationship 
>> would cause the table to be delete-connected to the same table 
>> through multiple relationships and such relationships must have the 
>> same delete rule (NO ACTION, RESTRICT or CASCADE).) '
>>
>> So, I looked it up in the DB2 docs and I understand where the error 
>> is coming from, but I don't see how to design around it.  What I want 
>> is to have tracks and mediafiles with unique IDs (across both 
>> tables).  The playable table should achieve that.  If the parent 
>> playable is deleted, I want the track or mediafile subclass (in 
>> Hibernate/Java terms) to be deleted as well.  If the parent track of 
>> a mediafile is deleted, I want the mediafile's trackid to be set to 
>> NULL.
>>
>> I think that I understand why the delete-connected restriction is 
>> there, but since I have the foreign keys in two separate columns and 
>> the parent rows of any involved track and mediafile rows must be 
>> dependent on different rows in the playable table, I don't think that 
>> it should be an issue for me (logically, anyway).
>>
>> Can anyone think of a workaround (or a better way to design the 
>> schema)?  I thought about using a shared sequence, but that's not 
>> avaiable either.
>>
>> Thanks for your help!
>> -Justin
>>
>>
>>
>>



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