How the proxy work actually? I totally can not see the hsql query in console but i can get the data. How can i enable the lazy=true? Which one is better proxy or laxy = true.

As I understand it, the different between lazy="true" and lazy="proxy" is that lazy="true" is property-level laziness, but ="proxy" is entity level. That is, when you access any property in an entity that has been retrieved via a default/lazy="proxy" association, the whole entity is initialized, except for properties that are lazy="true"; they're not retrieved from the database until they are accessed.

The default is better in most cases, because the most common situation is that you want all/most of the fields in an entity, and there's no point in going to the database once per property. For very large fields, blobs, clobs, etc., you might want to set lazy="true", so that the data is not retrieved unless actually needed.

(Note that in 3.1, lazy="true" has been renamed to lazy="no-proxy", presumably to reduce this sort of confusion)

How come the hibernate reference book does not talk about the thing that you mentionded here? Whe can i find this tutorial?

That's probably because hibernate is updated faster than the book is reprinted :) Read the ref docs of each version, as they come out.

In the 3.1 ref docs, sections 5.1.10 (brief) and 19 (whole thing) are the bits to read. Compare those with sections 6.1.10 and 20 in the 3.0 ref docs.

I am talking about many to one association.

1) I am using hibernate 3.0.5. I still do not understand the lazy=proxy VS lazy=true.

2) I will get red line in eclispe when i set the lazy="true"? But it exists in reference book.
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

2) I can not see the query if i set lazy=proxy. Why?

2) The 3.0 DTD at sourceforge doesn't mention the lazy attribute on many-to-one at all. Strange. In the downloaded source code, the 3.0 DTD in the 3.1.1 release doesn't allow lazy="true", but does allow lazy="no-proxy", which is the new name for the same thing. In the 3.0.5 release, the 3.0 DTD allows lazy="true". Eclipse's red line is probably dependent on which version of the DTD it's looking at.

1 + 2(b)) lazy="proxy" means that when any member of the proxied object is queried, the whole object is retrieved in one select statement. Until then, a fake (CGLib) version of the object is used. Any values that hibernate puts into the fake version (notably, the ID) are valid values, and when they're accessed, hibernate does not de-proxy the object. lazy="true" or lazy="no-proxy" issues the select as soon as the object is accessed.

This is from the ref docs, section 19.1:

Anyone can tell me why can not see the query if i set lazy=proxy but i can get the object. Why?