puzzled! help me

newpaul · **Joined:** Thu Aug 28, 2003 11:19 pm **Posts:** 17

three objects : tracker , topic ,message

relations of tracker and topic is one-to-many
relations of topic and message is one-to-many

now i need add a topic to tracker ,and at the same time add a message to topic

Code:

tk =(Tracker)session.load(Tracker.class,trackerid); 

Topic tp=new Topic();
tp.setTopicId(topicid);
tp.setTopicOwner(owner);
tp.setTitle(title);
tp.setTracker(tk);
tp.setState(-1);
tp.setCreatedBy("paul");
tp.setCreatedTime(new Date());
tp.setLastUpdate(new Date());

Message ms=new Message();
ms.setMessageId(new Integer(0));
ms.setCreatedTime(new Date());
ms.setCreatedBy("paul"); 
ms.setBody(message);
ms.setTopic(tp);

tp.getMessages().add(ms);
tk.getTopics().add(tp);

session.save(tp);

and run the code tp.getMessages().add(ms) throw a exception:java.lang.NullPointerException
at com.beaconsystem.catseye3.actions.SaveTopicAction.execute(SaveTopicAction.java:101)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:465)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1422)

how do i resolve it

steve · **Posted:** Fri Aug 29, 2003 8:17 am

Not nearly enough information here, but I'll give it a shot...

You are trying to access tp.getMessages(), where tp is a variable you just previously set to be = new Topic(). I'd be willing to bet that inside the Topic class you are not initializing the messages collection. Thus messages would be null and tp.getMessages() would return null. You can't call methods on a null reference...

christian · **Posted:** Fri Aug 29, 2003 8:38 am

If possible (this should be 99%), initialize your collections at declaration:

class Person {
String name;
Set addresses = new HashSet();
...
}

[/list]

newpaul · **Joined:** Thu Aug 28, 2003 11:19 pm **Posts:** 17

yes

tp.setMessage(new HashSet())
tp.getMessage().add(ms)

there is no error, but according to this way, only topic is inserted into database, message not!

why?

steve · **Posted:** Sun Aug 31, 2003 12:02 pm

Still not enough information here. How about posting your mappings, especially for how tracker, topic, and message relate to each other.

I would guess you have not appropriately set up cascading to acheive what you are looking for.

clarence_chiang · **Joined:** Tue Aug 26, 2003 10:17 pm **Posts:** 5

Hi,

I guess you should check for your cascade setting in the 1-n mapping in your tracker and topic mapping. Hibernate will only save the message for you in cascade="all" or cascade="save-update" with appropriate unsaved-value attribute set to message.

Clarence

newpaul · **Joined:** Thu Aug 28, 2003 11:19 pm **Posts:** 17

ok i resolve it thanks