How to map composite primary key?

[tdang]

One table looks like this:

create table t(
id int not null,
int fid not null,
int something,
primary key(id, fid))

As you see, the table has a composite key.

I have the primary key class (MyKeyPK) for a bean MyBean. The MyBean looks like this:

public abstract class AbstractBaseBean implements
EntityBean {

public abstract void setMyKeyPK(MyKeyPK pk);
public abstract MyKeyPK getMyKeyPK();

public abstract int getSomething();
public abstract void setSomething(int something);

public MyKeyPK ejbCreate(MyKeyPK pk) throws CreateException, EJBException {
setMyKeyPK(pk);

return null;
}

public void ejbPostCreate(MyKeyPK pk) throws CreateException, EJBException { }

public void setEntityContext(EntityContext context) throws EJBException { }
public void unsetEntityContext() throws EJBException { }
public void ejbActivate() throws EJBException { }
public void ejbPassivate() throws EJBException { }
public void ejbRemove() throws EJBException { }
public void ejbStore() throws EJBException { }
public void ejbLoad() throws EJBException { }
}

How can I map a composite primary key in ejb-jar.xml and jbosscmp-jdbc.xml?

Regards.

[dsundstrom]

You need a custom primary key class. I suggest you take a look at one of the EJB books; look for primary key class in the index.

[gummy]

Hi Dain,
I did use the primary key class I created, and I declared in the ejb-jar.xml file under that particular
entity as:

.
.
<prim-key-class>table1Key</prim-key-class>
.
.

but I am still getting an error when I started the server.

javax.ejb.ObjectNotFoundException: Object with primary key table1Key@4df1cf5b not found in storage

Do you know what I might do wrong?
David Li.

ps. thx for the comments on my other post, I am trying to read the docments on JBoss3.0.1 now. and in the progress of testing xdoclet to generate my ejb deployment scripts.

[gummy]

Hi Dain,
I did use the primary key class I created, and I declared in the ejb-jar.xml file under that particular
entity as:

.
.
<prim-key-class>table1Key</prim-key-class>
.
.

but I am still getting an error when I started the server.

javax.ejb.ObjectNotFoundException: Object with primary key table1Key@4df1cf5b not found in storage

Do you know what I might do wrong?
David Li.

ps. thx for the comments on my other post, I am trying to read the docments on JBoss3.0.1 now. and in the progress of testing xdoclet to generate my ejb deployment scripts.

[dsundstrom]

You could be doing lots of things wrong. It is very hard to get the primary key class correct (a lot of generators like JBuilder get it very wrong).

The two most important methods are equals and hashCode. Don't try to implement any inheritance in your pk classes; it is way more trouble then it is worth.

Here's some sample code. This may not be perfect; I writing it from memory: [pre]
public boolean equals(Object o) {
if(!(o instanceof MyPkType)) {
return false;
}
// will never be null
MyPkType myPk = (MyPkType)o;
return myPk.blah1.equals(this.blah1) &&
myPk.blah2.equals(this.blah2) &&
myPk.blah3.equals(this.blah3) &&
myPk.blah4.equals(this.blah4);
}

public int hashCode() {
int result = 17;
result = 37*result + (blah1==null ? 0 : blah1.hashCode());
result = 37*result + (blah2==null ? 0 : blah2.hashCode());
result = 37*result + (blah3==null ? 0 : blah3.hashCode());
result = 37*result + (blah4==null ? 0 : blah4.hashCode());
return result;
} [/pre]

[dokomesiter]

Might I suggest that it would be enormously helpful if the JBossCMP book simply changed one of the tables, such as gangster, from primitive key (integer gangsterId), to a composite primary key (GangsterKey{firstName,lastName}).

It seems there are many of us who have been beating our heads for many hours (or at least I have mine) on the vast multitude of ripple affects from such a seemingly "trivial" change for such a basic design pattern.

Stump point #1: primkey
primkey-field, primkey-class mismatch
(primkey omission)
Stump point #2: CMR
how to map CMR column name to multiple fields
Stump point #3: create
table generation failure
(turn off primary key constraint)
Stump point #4: exists
JBoss omits where: SELECT COUNT(*) FROM TBL WHERE
(still working on this one)
Stump point #5: DVC
etc. etc.

Cheers,

Chris

[dsundstrom]

I'm actually planning on writing a short article on the correct way to write a compoung primary key.