[ajug-members] Order of cascaded deletes with hibernate

[Les A. Hazlewood]

As a former Hibernate consultant (worked w/ Gavin, Steve, et. al), I'll
answer ;)

Hibernate does not support allowing you to control the order of cascade
execution.

Hibernate uses transactional write-behind algorithms for determining
which objects it needs to insert/update/delete and when.  This basically
means that it optimizes the order in which SQL statements are executed
automagically at the end of a transaction based on a number of things,
including dirty data, collection modification, etc.

Because Hibernate uses these optimization algos, it determines how
cascades will be executed, not the programmer.  This is the primary
reason why Hibernate is almost always faster than a comparable
appliation that uses hand-written JDBC calls.  It can do all sorts of
things like use the JDBC batch api, only execute sql upon transaction
commit, etc., all transparently to the programmer while increasing
performance.

However, because you need certain elements to be deleted before others,
this might be a red flag that what you require is more closely related
to business logic (your app requirements) and not raw persistence logic
(Hibernate's realm).  If this is the case, explicit manual deletion is
usually preferred since it will be obviously documented in your source
code, thereby clearly reflecting your application requirements.

Best regards,

Les

On Wed, 27 Apr 2005 12:30:17 -0400, "Roy Wells" <roy.g.wells at gmail.com>
said:
> To any hibernate gurus out there.
> 
> I'm having an issue with cascaded deletes in hibernate.  I would ask
> this on the hibernate forum but that place gives answers at a snails
> pace.  In fact someone else allready asked it there and got ignored.
> 
> Here is the setup: Class "A" is a parent to both "B" and "C", and has
> one-to-many collections of each.  Class "C" has a unidirectional
> many-to-one association with "B".  The one-to-many collections from
> "A" to both "B" and "C" are cascade delete.
> 
> The problem arrises when hibernate triggers cascade deletes from "A"
> to "B" and "C" it needs to delete "C" first but it doesn't.
> 
> Is there a way to control the order in which deletes are cascaded in
> hibernate.  Otherwise I guess i'll just turn off the cascade deletes
> and handle it with manual calls.
> 
> I also thought I might solve this with a Hibernate Interceptor, but
> i've read that calling back into the session and triggering additional
> operations from a hibernate interceptor is not supported.
> 
> Here is what the hibernate mapping essentially looks like.
> 
> <hibernate-mapping >
> 
>   <class name="A">
>     <id name="id"><generator class="native" /></id>
>     <bag name="bList inverse="true" lazy="true" cascade="all">
>       <key column="a_id"/>
>       <one-to-many class="B"/>
>     </bag>
>     <bag name="cList inverse="true" lazy="true" cascade="all">
>       <key column="a_id"/>
>       <one-to-many class="C"/>
>     </bag>
>   </class>
> 
>   <class name="B">
>     <id name="id"><generator class="native" /></id>
>     <many-to-one name="a" column="a_id" not-null="true"/>
>   </class>
> 
>   <class name="C">
>     <id name="id"><generator class="native" /></id>
>     <many-to-one name="a" column="a_id" not-null="true"/>
>     <many-to-one name="b" column="b_id" not-null="true"/>
>   </class>
> 
> </hibernate-mapping>
> 
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