Hi,

I am new to hibernate and right now I have some performance problems.
I want to change an already small web application which previosly used only properties and it didn't have any relation between tables. I tried to change this to one-to-many relation.
Previosly the application worked, but the interogations were made in the hard way. For example: I have a table customer and another table house. A customer can have many houses. For this reason a foreign key to customer was introduced by me in house.

Previosly to know the houses for one cusotmer the interogation was made through the HouseDao Object everytime. Now I have a field of type list in my Customer POJO and I want to get directly all the house through this list. I set to lazy-loading in the hibernate mapping file.

But after 2 or 3 interogation the application crash with this message:
"11:28:22,385 INFO [STDOUT] 11:28:22,370 WARN [OgnlValueStack] Caught an exception while evaluating expression 'accommodationUnits' against value stack
Caught an Ognl exception while getting property accommodationUnits - Class: ognl.OgnlRuntime
File: OgnlRuntime.java
Method: getMethodValue
Line: 935 - ognl/OgnlRuntime.java:935:-1
at com.opensymphony.xwork2.util.CompoundRootAccessor.getProperty(CompoundRootAccessor.java:106)
at ognl.OgnlRuntime.getProperty(OgnlRuntime.java:1643)
at ognl.ASTProperty.getValueBody(ASTProperty.java:92)
at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
at ognl.SimpleNode.getValue(SimpleNode.java:210)
at ognl.Ognl.getValue(Ognl.java:333)
at ognl.Ognl.getValue(Ognl.java:310)
at com.opensymphony.xwork2.util.OgnlUtil.getValue(OgnlUtil.java:190)
at com.opensymphony.xwork2.util.OgnlValueStack.findValue(OgnlValueStack.java:208)"


And I don't know in which direction I should go. Should I stick with the old method (all table fields are mapped als properties in the hibernate mapping file) or I should try to accomplish the associations also in the hibernate mapping file?

Any advice will be very appreciated.

Unfortunately, this exception trace is not quite clear. In fact, this might even be no problem with the Hibernate mapping at all. Try debugging the "getAccommodationUnits" method wherever it is to check the state of your persistent objects at that time. Also, make sure the session is open to make sure lazy loading works.

It would help to see the actual mappings and some of the DAO code in order to better help you.

Hi,

Sorry for my late answer.

Yes I try to implement the lazy loading in an application which use Struts2, Spring and Hibernate. But when the lazy property should be initialized the connection is closed.

I spent some time and I hound that I should implement a well-known pattern in the hibernate world but I don't know exactly how.
Some information are on this link:
http://www.hibernate.org/43.html

If someone knows a tutorial or an example, please let me know.

Indeed very common problem. You will have to go through a small checklist on your current code:

- do not open or close session in DAOs
- do not start or end transactions in DAOs or services
- use some ThreadLocal strategy to get the session (there is a small HibernateUtil class around the internet, or you can configure the session to be RESOURCE_LOCAL (JPA)

This will get you going to implement the filter that the documentation page you cited explains. This filter is intended to keep the session open until after the page is rendered, therefore providing lazy loading for as long as it can be used.