Lazy update (update only the "not null" members)

jeremychone · **Posted:** Sat Jun 10, 2006 4:49 pm

Hibernate version: 3.1.3
Mapping documents: Annotation 3.1.0 Beta10
Name and version of the database you are using: Mysql 5.0 (windows)

Is there a way to update only the "not null" values of an object. I have been looking at "dynamic-update", but this is not really what I need.

I would like hibernate to generate/execute an update statement with only the "not null" properties of an object (completely ignoring the null properties)

My client is sending a partial object (in XML) and I would like to avoid reloading the whole object on the server, but just treat the partial object as the delta to be updated.

Ideally, I would see this as a runtime parameter on the "session.update" method.

Am I missing anything obvious?

Jeremy,

damnhandy · **Posted:** Sun Jun 11, 2006 1:14 pm

While it would be a bit more work on you end, you could generate a DML-style update statement to execute your query:

http://www.hibernate.org/hib_docs/v3/re ... tch-direct

This way you can control exactly what fields are updated. You can take this further by looking at the mapping package:

http://www.hibernate.org/hib_docs/v3/ap ... mmary.html

Using the PersistentClass object, you can find all properties which are "not null" and generate an HQL statement from that. A little complicated, yes. But other than that, I can't htink of anything that could update only "not null" fields exclusively. Now if only we could do updates via Criteria :)

Ryan-

scarface · **Joined:** Sun Jun 04, 2006 1:58 am **Posts:** 136

You can define you sql with required colums ( not null type in ur case)

http://www.hibernate.org/hib_docs/v3/re ... erysql-cud

jeremychone · **Posted:** Sun Jun 11, 2006 7:29 pm

scarface wrote:

You can define you sql with required colums ( not null type in ur case)

http://www.hibernate.org/hib_docs/v3/re ... erysql-cud

Thanks, I was hoping to do something once for all my classes. But I will look into custom sql per class if I cannot find a more generic way.

Tx a lot.

damnhandy · **Posted:** Sun Jun 11, 2006 8:27 pm

As I mentioned before, you can be a bit more generic by looking at Configuration and getting a hold of a PersistenClass instance. By doing this, you can find all properties which map to columns that are not null. Here's some example code I posted in another thread:

Code:

Configuration cfg = HibernateUtil.getConfiguration();
StringBuffer hqlQuery = new StringBuffer();
PersistentClass pc = cfg.getPersistentClass(SomeEntity.class.getName());
Iterator properties = pc.getPropertyIterator();
while(properties.hasNext()) {
   Property property = (Property) properties.next();
   Iterator columns = property.getColumnIterator();
   while(columns.hasNext()) {
      Column column = (Column) columns.next();
      if(!column.isNullable()) {
         /*
          * Insert your own code to add this property to your HQL query
          */
      }
   }
}

Once you've generated your HQL, or SQL for that matter, you can simply execute an update:

Code:

Session session = HibernateUtil.getCurrentSession();
int updatedEntities = s.createQuery(hqlQuery.toString()).executeUpdate();

While not as elegant as some type of mapping attribute, it will do the trick. It's generally a good idea to generate the query strings at startup to avoid any performance hot of creating a query over & over again.

jeremychone · **Posted:** Sun Jun 11, 2006 9:10 pm

Tx Damnhandy,

I was responding to the custom sql solution. I was still trying to understand yours (I am not deeply familiar with the Hibernate "internals" yet). Thanks a lot for the extra help. This is very helpful.

BTW, I was referring to the "java properties" being not null and not the columns. So, in a pure update, I do not really need to check if the column is nullable, but rather if the object instance property has a value.

Anyway, thanks a lot for your help.

Jeremy,

damnhandy · **Posted:** Sun Jun 11, 2006 10:40 pm

Just FYI Jeremy, the Column.isNullable() method will return true if the mapping file declares a property's not-null attrubute as true. The PersistentClass represents what is declared in your mapping file, it does not look at the database table. I only bring this approach out as I have to do something very similar before.

Ryan-

mmonette · **Joined:** Wed Nov 16, 2005 10:58 am **Posts:** 5

You may find it useful to look at the ClassMetaData class as well. It gives you much of the same information as PersistentClass, and doesn't require that you have the Configuration available. You can get access to the field values through ClassMetaData.getPropertyValue(...).

mmonette · **Joined:** Wed Nov 16, 2005 10:58 am **Posts:** 5

I forgot to mention how to get the ClassMetaData. You can get it per class from the session factory, either by .class or by name.
ex. sessionFactory.getClassMetaData(Foo.class) or
sessionFactory.getClassMetaData("package.name.Foo")