Lazy-loading a Lob

fyaa · **Joined:** Wed Nov 10, 2010 2:28 pm **Posts:** 2

Hello,

I crawled hours now through the net searching a solution, so I finally ask you my question:

I've got a class files which contains a clob. Well it's a clob and clobs are used for large data, so I don't want to load it right with the files, if I'll only get an overview of them.

Code:

@Entity
@Table(name = "FILES")
public class File implements Serializable {

   @Id
   @Column(name = "ID")
   private int id;

   @Lob
   @Column(name = "DATA")
   @Basic(fetch = FetchType.LAZY)
   private char[] data;

   // ...
   // getter and setter
   // ...

}

Usually, i'd expect from Hibernate, that it will load the clob, when I first access it.
Selecting a Lob with JDBC, you also only get a reference, from which you can load the data with a stream.

But with some reason, this doesn't work directl with Hibernate, as I had to read.
In the documentation I read something of a "Bytecode Instrumentation".
Sadly I don't have a clue what this is.. so what it es, why it is needed, nor a tutorial or example how it's inserted.

I have to add that i work with Eclipse.

So i would really really be happy, if someone could tell me how the thing works :).
I don't get a point to start with.

Thanks in advance!

r · **Joined:** Fri Oct 08, 2010 8:44 am **Posts:** 130

Try to set "hibernate.bytecode.use_reflection_optimizer" system property to "false".

hallmit · **Posted:** Fri Nov 12, 2010 6:10 am

fyaa wrote:

But with some reason, this doesn't work directl with Hibernate, as I had to read.
In the documentation I read something of a "Bytecode Instrumentation".

Hibernate uses a runtime proxy generation to provide lazy loading and this works only for entity associations and collections. if you want to load an individual scalar property you must use a build time bytecode instrumentation (lazy loading with interception)

You can also replace your char[] field by java.sql.Blob (or Clob), according to Hibernate the driver implementation of Blob and Clob provide lazy loading by definition (but i've encountered a lot of problems with PostgreSQL and MySQL databases. see viewtopic.php?f=1&t=1006742 and viewtopic.php?f=1&t=1005584)

fyaa wrote:

Sadly I don't have a clue what this is.. so what it es, why it is needed, nor a tutorial or example how it's inserted.

to enable interception, the bytecode of your classes must be instrumented after compilation like shown here viewtopic.php?f=1&t=1005893