[jboss-user] [Persistence, JBoss/CMP, Hibernate, Database] - Two-way association problem

[li.ni@helmet.fr]

Hi, 

I have met a problem using EntityHome with Seam, I have found a solution by modifying a setter but I want to be sure it is the proper way to do it.


In order to implement a function “Post a topic in a forum”, I have created 2 EntityBeans : Subject and Message. There is a oneToMany (two-way association) relation between Subjet and Message.



public class Subject implements Serializable {

...

private List associatedMessages = new LinkedList();


@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "ownerSubject")

@OrderBy(value = "messageId ASC")

public List getAssociatedMessages()

{

return associatedMessages;

}

public void setAssociatedMessages(List associatedMessages)

{

this.associatedMessages = associatedMessages;

}

...


}


public class Message implements Serializable {

...

private Subject ownerSubject;

@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)

@JoinColumn(name = "OWNER_SUBJECT_ID")

public Subject getOwnerSubject()

{

return ownerSubject;

}

public void setOwnerSubject(Subject ownerSubject)

{

this.ownerSubject = ownerSubject;


}

}



When a Subject instance is created, at the same time a 1st Message instance is created too and added to the List the subject, as shown in createSubject2() of the SessionBean SubjectHome



@Name("subjectHome")

public class SubjectHome extends EntityHome

{

...

@In(required=false)

MessageHome messageHome;



public void createSubject2()

{

this.messageHome.getInstance().setOwnerSubject(this.getInstance());

this.messageHome.persist();

this.logger.info("NUMBER OF ASSOCIATED MESSAGES : " + this.instance.getAssociatedMessages().size());

}

...

}


I've checked: 2 instances were successfully persisted, so in the datebase, 2 new rows were inserted in Subject table and Message table with no problem.


However in the console :

INFO [SubjectHome] NUMBER OF ASSOCIATED MESSAGES : 0

And when I navigate to the webpage which is used to show something of corresponding message of a Subject i met such error:

CODE:

#{subject.associatedMessages.get(0).submitTime}

ERROR:

/subjectList.xhtml: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0



So I add a line in the Setter in my Message EntityBean :


public void setOwnerSubject(Subject ownerSubject) {

this.ownerSubject = ownerSubject;

this.ownerSubject.getAssociatedMessages().add(this);

}

This solves our problem, the new message is well in the subject List attribute without having to open a new session.

I just want to verify if it's ok to add additional line in Setter of EntityBean, just like what I did ? Thank you!

Regards

Li

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