JPA -- How can I turn off the caching for an entity?

Question

Hi,
I have a problem that I will illustrate with a simplified example. I have created an entity:
@Entity(name="Customer")
@Table(name="CUSTOMERS")
public class Customer implements Serializable {
}I have also set the collowing properties in persistence.xml:
<property name="toplink.cache.type.default" value="NONE"/>
<property name="toplink.cache.size.default" value="0"/>
<property name="toplink.cache.type.Customer" value="NONE"/>
<property name="toplink.cache.size.Customer" value="0"/>
<property name="toplink.cache.shared.Customer" value="false"/>And then I run the following code:
Customer cust = em.find(Customer.class, 1L);
System.out.println(cust);
cust = em.find(Customer.class, 1L);
System.out.println(cust);The problem: the second call to em.find does NOT generate a query to the database. Here's a fragment from the console log:
[TopLink Fine]: 2007.05.11 02:55:05.656--ServerSession(2030438)--Connection(5858953)--Thread(Thread[Main Thread,5,main])--SELECT ID, SEX, NAME, MANAGER FROM CUSTOMERS WHERE (ID = ?)
     bind => [1]
Customer: id=1, name=Customer #1, sex=MALE
Customer: id=1, name=Customer #1, sex=MALECan anyone help me? Why isn't the caching turned off? I tried various combinations of properties. Nothing worked. I was expecting to see two queries to the database. I can see only one.
I tried with TopLink Essentials Version 2 Build 39 and Version 2 Build 41.
Best regards,
Bisser

Answer 1

The cache is likely turned off, but you can't tell because you are using the same transactional EntityManager instance for the two queries. The EntityManager requires its own cache for object identity and transactional purposes, as once you read an object in through the EM, the spec requires that all subsequent reads return the same instance. Only the EntityManager refresh will cause a refresh, that or setting your queries to use the toplink.refresh and toplink.cache-usage query hints.
I would strongly recommend you use a query cache for performance, but there are of course reasons why one might not be the best option.
http://weblogs.java.net/blog/guruwons/archive/2006/09/understanding_t.html
is a good blog on understanding the caching used In TopLin Essentials.
Best Regards,
Chris