Alvin,
OK then here is the thing:
When you use EJB relationships, you don't have to think only relational
database but also Object Oriented database.
I mean you don't have to store in an entityA field the PK of entityB but
rather say to the system, (in this case the EJB container) my entityA
instance is linked to this instance of entity B and the system (OO DB or
the container is taking care of the persistency of that specific
instances' relation).
For example:
EntityA represents BANK's users (PK= String userID + String bankID)
EntityB represents BANKs (PK= String bankID).
A Bank may have several users within the bank.
Suppose you want to create a EJB relationship between users and banks.
So you create a CMR field in EntityA called rBank. This relationship
needs to be persisted so you specify in the deployment descriptor that
the relationship is related to the table Users, column field bankID
(which is, from a relational DB point of vue, a FOREIGN KEY).
You need to "tell" the container how it should persist the relationship.
The DD is there for that.
Of course you have that column represented in the entityA as a CMP field
(bankID) so you may (NOT AN OBLIGATION) have defined (your IDE may have
done that for you automatically) a SET method for that CMP field.
In EntityB you have a CMR field called rUsers for which the getRUsers
method return a Collection of EntityA instances.
Again here, that CMR is linked to the CMP field bankID in the table BANK
for persistency purposes.
Note: CMR fields like CMP fields can have getters and setters.
Now, you want to create a new user.
>From the EntityA home interface you use the create method which will
return you a new EntityA instance.
Within the ejbCreate method of EntityA you may initialise the
relationship with a bank's instance. You can't use the setBankID of
EntityA (THAT's THE RULE in the SPEC) but you need to ge the bank's
instance (findByPK) and apply the method:
instanceB.getRUsers().add(this).
Of course I do not recommend to do that there.. But rather in a
SessionBean.
So in the session bean:
EntityA entityA = null;
EntityB entityB = null;
Try
{
entityA = entityAHome.create(new PK);
entityA.setXXX(...) for CMP fields not being part in a relation
(you can do the setter in the ejbCreate method).
entityA.setBankID(bankID); /// THIS WILL CAUSE AN EXCEPTION
entityB = entityBHome.findByPK(bankID);
entityB.getRUsers().add(entityA); //here the container will
update CMP field bankID in entityA with the right info based on the info
provided in the deployment descriptor).
}
Note: I'd recommend you not to provide any setters for CMP-CMR fields to
avoid any tentation!!
Note: in the case of a N-M table relationship, you need to have a
intermediate table (typical database technique) and CMR fields in
entnityA/B needs to be "physically" linked (in the DD) to that
intermediary table.
Daniel
-----Original Message-----
From: Alvin Wang [mailto:[EMAIL PROTECTED]]
Sent: lundi 11 mars 2002 16:14
To: Daniel De Luca; [EMAIL PROTECTED]
Subject: RE: An CMR related exception
Daniel, I feel that my problem is not initializing a PK, but any field
that is mapped to a CMR. Again, the exception is as below:
"javax.ejb.EJBException: When a cmp-field and a cmr-field (relationship)
are mapped to the same column, the setXXX method for the cmp-field may
not be called. The cmp-field is read-only."
Yeah, the XXX happens to be a foreign key in my case
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]]On Behalf Of Daniel De Luca
Sent: Monday, March 11, 2002 9:52 AM
To: [EMAIL PROTECTED]
Subject: Re: An CMR related exception
Alvin
Yes entityA is an existing instance which has a PK.
It won't be possible for you to use your PK in a relationship between
entities. If your instanceA PK and instanceB PK are used for the
relationship between each other, you need to change the PK of the
corresponding entities to make them relationship independent. This mean,
create a new CMP field in both entities that will be used as PK. Then
use the old PKs as "normal" fields (non used as PK) in order to be able
to used them as CMR and without being forced to initialize them in the
ejbCreate method.
If this is not giving you a solution to your problem, could you send the
code of your entities (puttin in comment which are the field that are
used in your relationship and which one are PKs).
Hope this help
Daniel
-----Original Message-----
From: Alvin Wang [mailto:[EMAIL PROTECTED]]
Sent: lundi 11 mars 2002 15:44
To: Daniel De Luca; [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Subject: RE: An CMR related exception
Daniel, I read the section you pointed out. I did not find either how it
is related to my problem and how your solution solves my problem.
in "entityBRef.getREntityA().add(entityARef)", is entityARef an existing
Bean A instance initialized with PK? Then when/how did that XXX field
INITIALIZED?
I'm a little slow. Please give me details. Thanks!
-----Original Message-----
From: Daniel De Luca [mailto:[EMAIL PROTECTED]]
Sent: Monday, March 11, 2002 4:08 AM
To: [EMAIL PROTECTED]
Subject: RE: An CMR related exception
Alvin,
Yes that's right.
Why? Well that's how the specs are defined and how the App Server
container have to do things. Check the EJB 2.0 specs for more details:
10.3.8 Collections managed by the Container, 10.3.6 Semantics of
assignment for relationships
Daniel
-----Original Message-----
From: Alvin Wang [mailto:[EMAIL PROTECTED]]
Sent: samedi 9 mars 2002 2:23
To: Daniel De Luca; [EMAIL PROTECTED]
Subject: RE: An CMR related exception
Deniel, thanks for replying. Do you mean
"entityBRef.getREntityA().add(entityARef)" will initialize that field?
Why? Or when and how that field will be initialized in later time?
Please give more details!
Thanks!
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]]On Behalf Of Daniel De Luca
Sent: Friday, March 08, 2002 11:58 AM
To: [EMAIL PROTECTED]
Subject: Re: An CMR related exception
Alvin,
You can't apply a Set method on a cmp-field that is used in a
relationship between 2 entities. You don't necessarily need to
initialize that field in the ejbCreate method. What you have to do is
create the Entity bean and initialize only the PK.
Then suppose EntityA has a relation with EntityB and the CMR fields are
rEntityB (in EntityA) and rEntityA (in EntityB) In order to "set" the
relationship between the 2 you need to use the
entityBRef.getREntityA().add(entityARef).
After that your CMP-field will be up to date.
I would suggest you to read the EJB 2.0 Spec, everything is explained
there.
Hope this help.
Daniel
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]] On Behalf Of Alvin Wang
Sent: vendredi 8 mars 2002 16:12
To: [EMAIL PROTECTED]
Subject: An CMR related exception
Hi! I am using Weblogic 6.1 SP2 and EJB 2.0. I built a CMR between two
Entity Beans. However, I got the following exception while running:
"javax.ejb.EJBException: When a cmp-field and a cmr-field (relationship)
are mapped to the same column, the setXXX method for the cmp-field may
not be called. The cmp-field is read-only."
However, in the ejbCreate() method in CMP in EJB 2.0, I have to use
setXXX method to initialize the XXX cmp-field. Am I wrong?
Can any guru help? thanks!
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