How to code the ejbCreate() method without initailizing primary key?

Question

Hi all,
I've just started learning about EJBs, and now am at the stage of learning how to create, deploy and test a CMP Entity Bean.
Ran into a problem which I'm hoping someone can help out with.
I'm using SQL Server 2000 as my backend database, and have created a simple table called TEST with 2 fields, id and name. id is set as the primary key, and as an identity conlumn. What this means is that when we do inserts, we don't need to specify a value for the id column. SQL Servers automatically generates that value.
Here's my ejbCreate method in my bean class:
public Integer ejbCreate(String name) throws CreateException {
    this.setName(name);
}When I tried to run the create method from a web client, I got this error:
javax.ejb.CreateException: [EJB:010148]In EJB 'SampleEJB', the primary key field 'id' was not set during ejbCreate. All primary key fields must be initialized during ejbCreate. at weblogic.rmi.internal.ServerRequest.sendReceive(ServerRequest.java:186) at weblogic.rmi.cluster.ReplicaAwareRemoteRef.invoke(ReplicaAwareRemoteRef.java:284) at weblogic.rmi.cluster.ReplicaAwareRemoteRef.invoke(ReplicaAwareRemoteRef.java:244) at everbright.ejb.SampleEJB_uzc4wg_HomeImpl_813_WLStub.create(Unknown Source) at jsp_servlet.__index._jspService(__index.java:152) at weblogic.servlet.jsp.JspBase.service(JspBase.java:33) at weblogic.servlet.internal.ServletStubImpl$ServletInvocationAction.run(ServletStubImpl.java:996) at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:419) at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:315) at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.run(WebAppServletContext.java:6452) at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:321) at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:118) at weblogic.servlet.internal.WebAppServletContext.invokeServlet(WebAppServletContext.java:3661) at weblogic.servlet.internal.ServletRequestImpl.execute(ServletRequestImpl.java:2630) at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:219) at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:178)
So it seems like I can't leave the id field uninitialized in the ejbCreate method. However I don't know what to initialize it with either, because in order to know what value I need to initialize it to, I'll need to run a db query to retrieve the next primary key value for the id field. This doesn't sound very efficient to me.
I tried to initailize it to null, but that gave me a NullPointerException.
Why do we need to initialize the primary key field in ejbCreate? Should the container do the insert and then get it from the table accordingly?
Is there any other way I can get this set-up working?
Thanks!

Answer 1

Hi Fusion777,
Ya, I've been searching around forums for an answer also. Apparently this is indeed a problem that has no general solution. It depends on 2 factors:
1) Whether or not the database supports autogenerate key (which most does) and how (Oracle does it by sequences while SQL Server by identities)
2) Whether or not the application server supports 1).
In my case, I'm using SQL Server and Weblogic Server 8.1 and most fortunately, Weblogic does support identities and sequences. Just define the <auto-key-generation> stanza in your weblogic-cmp-rdbms-jar.xml deployment descriptor, as follows:
<automatic-key-generation>
     <generator-type>ORACLE</generator-type>
     <generator-name>test_sequence</generator-name>
     <key-cache-size>10</key-cache-size>
</automatic-key-generation>
<automatic-key-generation>
     <generator-type>SQL-SERVER</generator-type>
</automatic-key-generation>
<automatic-key-generation>
     <generator-type>NAMED_SEQUENCE_TABLE</generator-type>
     <generator-name>MY_SEQUENCE_TABLE_NAME</generator-name>
     <key-cache-size>100</key-cache-size>
</automatic-key-generation>I've tried that and it works :-)
I gather from your reply that those who are using JBoss are equally fortunate :-)
So I thought I'll share this in case some other poor fellow is facing the same problem as we are. At least worse come to worse, he'll have the option of switching to either JBoss or Weblogic and know that it works in both :-)
Some other users seem to be against the idea of using auto-generated keys for precisely the reason that it is not a standard across database and application servers. See this thread:
http://forum.java.sun.com/thread.jspa?forumID=13&threadID=329896
I've in fact stopped working on EJB 2.0 and am exploring something called Hibernate, which seems to have a more generic way of dealing with the auto-generated key issue. In fact, I've heard news that EJB 3.0, which is the upcoming standard for EJB, will be heavily inspired by Hibernate as far as CMP Entity Beans are concerned.
You can check out Hibernate at http://www.hibernate.org.