Hi,

I've read the hibernate docs and from what i understand if i the set the tag dynamic-update = true, then it should only generate a SQL statement that updates the actual attributes that have changed. I'm also using optimistic locking (version number) and even if i don't update any attributes on an object and call the session.update() method as listed below, the version number is incremented by 1 and the object is updated.

I thought that he desired result would be that Hibernate would check that the object has not changed and would not issue an update statement.
If i had a collection of objects you would expected only the objects that had changed, would be updated and the unchanged objects would not for performance. I also turned on the property show_sql=true so i see what sql statements that were being issued by Hibernate

Hibernate: update Drp set version=? account_id=?, type=? where drp_id=? and version=?

If it Hibernate was just updating the version, i would have expected that as i had set dynamic-update = true that the log would have shown the following instead.

Hibernate: update Drp set version=? where drp_id=? and version=?

I guess i'm unsure if i am doing something wrong or if Hibernate doesn't support this type of functionality that i am describing. I would greatly appreciate some help. List below SW, code and mapping docs.

Regards
Mark


Anyhow, i using
Hibernate 2.1.2
mysql 4.0.12 win
WSAD 5.1.1

Update code.
--------------
session = sessionFactory.openSession();
tx = session.beginTransaction();
session.update(myObject);
session.flush();
tx.commit();


Mapping Documents
-------------------------
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

<class name="com.thenational.model.Drp" table="Drp" dynamic-update="true" >

<id name="drpId" type="long" unsaved-value="null" column="drp_id">
<generator class="identity"/>
</id>

<!-- Use a version number for optimistic locking -->
<version name="version"
column="version"
type="integer"/>

<property name="accountId" column="account_id" />

<property name="type" not-null="true"/>

</class>

</hibernate-mapping>

Did you find an answer to your problem? I also have the same problem.
Gavin told me the following in this thread http://forum.hibernate.org/viewtopic.php?t=931327.



Which was not that helpful :)

This is from the docs:

Is it really neccessary to use dynamic-update in your case? There is no performance difference that you can measure and unless you have some weird triggers, I don't see a reason why the whole tuple shouldn't be updated.

Dynamic-update can only work if the changes occur inside of a session scope. If you reattatch an object using update, Hibernate has no way to determine which properties are dirty, and will update all of them.

So this means I have to load the object from the database before setting the fields. If I want to have dirty checking.

If I have for example



If I know the primary key then I should be able to do this



And this should generate an SQL that only updates the field I set (name).

Or am I missing something?

How would hibernate know what has got changed. You implement the setName yourself; after you call all your set and give your object to hibernate to save, there is noway for hibernate to know on what fields you have called the set.

It can only check with the database what the values there for these fields and do a dynamic update based on the database state.

Or you can set select-before-update="true"

I thought hibernate did some enhancements to the class so that it can detect changes in all cases. I guess I have to learn CGLIB and ASM. I'm going to read this http://www.open-lab.com/ppolsinelli/hibernateWorks.pdf maybe it will make things clearer.

Hibernate does _not_ do any enhancements to your base class. The only thing it does is - if you use proxys - generate a new subclass of your class in memory to use as a proxy. Just use your debugger and check it, the classes you get back are just normal instances of your class if you don't use proxys.

So with a proxy I would get the behaviour I need?

No. You can not use dynamic-update in combination with detatched objects.

ok thanks

yes, you can, use select-before-update="true"

Okay, of course :)