Hi,

I need some basic informations on the way hibernate is interacting with the second level cache. I'm using hibernate 3.1.2 with oscache from the distribution.

Example:
I have 3 persistent classes A,B and C. Class A has a collection of B and a 1:1 relation to class C. The 2nd level cache settings for all classes and relations are read-write. Every class has its own 2nd level cache region.

Question 1:
When hibernate puts an instance of A to the 2nd level cache does it still have the filled collection of B's and the relation to C in the way of complete instances of B's and C or are the objects disconnected from A and put in there own 2nd level cache regions?

Question 2:
When 1:n or n:m relations are declared to be cached what is cached? Are the complete referenced objects cached? If the referencend class allready has its own 2nd level cache region is there a way to use this instead of creating a new 2nd level cache region for the relation?

It would be very kind if somebody can help me.

Tanks in advance.
Alex

Objects are "dehydrated" before being stored in cache, meaning individual properties (including associations) are turned into serialized objects. When an object is loaded from cache, it is "rehydrated" into a regular POJO (or a proxy to it).
This way to concurrent sessions accessing the 'same' object are actually accessing two separate instances (both rehydrated from cache).

So question 1 : A is stored to cache, A's Bs are stored to their cache region, and so is C. A dehydrated state containts C's ID.

question 2 : if a 1-n or m-m is relation is cached, only the association is cached, not the objects themselves. So If A as many Bs and the A to B relation is cached, and if you the Bs have been expired from cache, calling A.getBs() will end up in one request for each individual B.

Disclaimer : I've not read not understood nor written Hibernate's whole code so I might be wrong. If a guru reads this and if I'm wrong, feel free to flame me :)

Tank you very much for your help.
I was hoping that the cache would behave this way.