Question

I have a property on a domain object that is declared in a many-to-one element. The basic syntax of this property looks like this:

<many-to-one name='propertyName' class='propertyClass' fetch='select' not-found='ignore' lazy='proxy' /> 

Now, the idea is to have Hibernate NOT eagerly fetch this property. It may be null, so the not-found ignore is set.

But, Hibernate, upon loading the class containing this association, takes it upon itself to load the actual class (not even a proxy) instance when the parent class is loaded. Since some properties are over 1MB in size, they take up a lot of the heap space.

If, however, not-found is set to exception (or defaulted to exception), the parent classes which have this property do load a proxy!

How can I stop hibernate from not loading a proxy, while still allowing this property to be null?

I found lazy=no-proxy, but the documentation talks about some sort of bytecode modification and doesn’t go into any details. Can someone help me out?

If it matters, it is the Java version of Hibernate, and it is at least version 3 (I can look up the actual version if it helps, but it is Hibernate 3+ for now).

I didn’t specify earlier, but the Java version is 1.4. So, Java annotations aren’t supported.

Answer 1

If the other end of the association can be null, I believe hibernate must query for the association end in order to determine if it should use a proxy or not (no need for proxy if the other end is null). I can’t find the reference to this right now, but I remember reading it somewhere.

In order to provide lazy-loading of fields the documentation refers to bytecode enhancements on fields at buildtime: Using lazy property fetching. Here is an excerpt:

Hibernate3 supports the lazy fetching of individual properties. This optimization technique is also known as fetch groups. Please note that this is mostly a marketing feature, as in practice, optimizing row reads is much more important than optimization of column reads. However, only loading some properties of a class might be useful in extreme cases, when legacy tables have hundreds of columns and the data model can not be improved.

Lazy property loading requires buildtime bytecode instrumentation! If your persistent classes are not enhanced, Hibernate will silently ignore lazy property settings and fall back to immediate fetching.