Why it's not possible to lazy initialize many-to-one mappings? Because now hibernate makes a lot sql queries, of whitch data is not used.
For example:
Item
{
Set subItems; // one-to-many
String name;
};
SubItem
{
SubItemType subItemType; //many-to-one
String name;
};
SubItemType
{
String name;
};

And now imagine Item has 100 subitems. I execute query "from Item it left outer join fetch item.subItems where it.name=:name";
And hibernates makes 1 + 100 queries for this select. If many-to-one mapping would be lazy, it'l make only 1 query and other querys only if I need subItemTypes. This is a big performance penalty I think.

And there are a lot of examples where lazy many-to-one is hitting on performance (object whith nested parents for example).

maybe because Hibernate can do lazy loading even for to-one assocations.

Just read the reference guide again

Reading reference once more, I found out, that to make many-to-one's lazy, you have to make a proxy for the class you are mapping (in my example to make proxy for SubItemType), because many-to-one doesn't have any property, whitch says about lazy loading. So in other words you have to make proxy for all your classes (in case you'll need lazy many-to-one in future). Is there any draw backs in such a move (exept those, that are written in manual - casting)? Is there any performance loss?

the class can be it's own proxy by:
1- specifying lazy="true" in the class element
or- specifying proxy="theNameOfTheMappedClass"
2- coding a defaut constructor in your pojo

so there are no additionnal classes to write