| Author |
ManyToMany merge problem
|
Maria Michael
Greenhorn
Joined: Sep 07, 2011
Posts: 18
|
|
Hello,
I have the following relationship:
An interview has many participants
A participant can be in many interviews
I resolved the relationship with an intermediate table in the database INTERVIEW_PARTICIPANT.
The following is the annotations in the Interview.java
The following is the annotations in the Participant.java
When I select the participants in the Interview, on saving (em.merge()) it prompts an error.
Summary of the error:
My JSF code:
Any ideas cause I really don't understand the problem from the stacktrace?
Thanks.
|
 |
Manuel Petermann
Ranch Hand
Joined: Jul 19, 2011
Posts: 175
|
|
You need to initialize the List.
JPA doesnt know which list implementation to choose.
Try:
if you want an ArrayList.
Edit: By the way this applies for one to many relations as well.
Edit2: I forgot to mention. You dont need to initialize it inside the class. It just has to be initialized before you do anything with it in jpa context.
|
Please correct my English.
|
|
Maria Michael
Greenhorn
Joined: Sep 07, 2011
Posts: 18
|
|
Manuel thank you for your reply.
I initialised the list in both the entity classes as you said.
Still the problem exists. I manually added data in the relationship via the SQL SErver database.
When I deploy the application the list shows correctly the selections based on the keys I entered in the database. If I just save without changing anything the error occurs.
BUT If I remove all selections from my jsf page the Save button works! and in the database what I previously entered is correctly removed.
My thinking is that at least it recognised the manytomany relationship.
Perhaps the entitymanager does not handle the lists correctly? I also tried Collection but still the same problem exists.
btw I do not have a class for the intermediate table-relationship as i read jpa handles it via the lists. Do I need a class?
Also before calling the entitymanager.merge() I print the list of participants and it shows the correct values.
Thank you.
|
|
James Sutherland
Ranch Hand
Joined: Oct 01, 2007
Posts: 550
|
|
Can you include the full stack trace, code where you call the merge, and what version you are using (did you try the latest EclipseLink release?).
Do you have a null in the collection, or a instance of a class that is not mapped?
Do other operations and class work? What is special about this case?
|
TopLink : EclipseLink : Book:Java Persistence : Blog:Java Persistence Performance
|
|
Maria Michael
Greenhorn
Joined: Sep 07, 2011
Posts: 18
|
|
Sure thank you,
The stacktrace:
My code in the controller bean
My code in the AbstractFacade.java (that has all operations done by the entity manager - yes I am using the code from the CRUD application Netbeans generated for me. It was a good starting point for me as a beginner
EclipseLink version (No I haven't tried to upgrade anything so that I don't mess up anything that I managed to make it work so far :S sad i know)
I think no I don't have a null in the collection I would know when I was printing it right?
Does it matter that I don;t have an entityclass for the intermediate table? I am sure the many to many works because it removes the entries from the database when I clear the list. but to insert new, or make changes it crushes.
It is the first time I ever tried @Manytomany relationship, so far onetoone and onetomany relationships in my application work just fine.
Thank you for your time.
|
|
Maria Michael
Greenhorn
Joined: Sep 07, 2011
Posts: 18
|
|
Solved the problem!!!
As I couldn't find many similar posts in google as my problem here, and my java code looked correct I thought the problem might be on the underlying database design.
My design was as following:
Interview table - Interview-Participants table and the Participant table. I figured there might be a problem that the many is on a table part of an aggregate relationship (Person - Participant).
Therefore I made the many to many relationship between the Interview table and the Person table and made all the necessary changes in my code.
This solved the problem even though I don't really understand why.
Thank you for your help.
|
|
James Sutherland
Ranch Hand
Joined: Oct 01, 2007
Posts: 550
|
|
Odd, what was the code that did not work vs the code that did?
You may want to log a bug and include both versions of your code, a null-pointer should never be occurring in merge, although it sounds like you may have mapped something wrong.
|
|
Maria Michael
Greenhorn
Joined: Sep 07, 2011
Posts: 18
|
|
Sorry for not replying earlier.
What I modified was the mapping of objects to the tables in the database as I described earlier (my post on June 7).
No code was modified other than the code to reflect the new way of mapping.
Hope this helps someone with similar problem.
|
|
 |
|
|
subject: ManyToMany merge problem
|
|
|
0
