Boyd, First off, I should note that I haven't actually used EJB since about 1.1 or so and have only been casually keeping up with some of the specs. Therefore, some of what I say may be a bit out of date. Please ingest large granules of salt while reading this.
What you're referring to is actually "CMP Entity Beans" (Container Managed Persistence). What you want can be achieved by using "BMP Entity Beans" (Bean Managed Persistence), where you write JDBC (or JDO or Hibernate or...) code in the Entity bean for accessing the database however you like. Essentially, a BMP Entity bean can be used to represent an arbitrarily complex data model but there are drawbacks -- you have to write and maintain much more code, performance may not be as good as with CMP (or such was the case when I last used EJB), and so forth. I was under the impression that EJB 2.0 introduced a query language (EQL) allowing very sophisticated mappings using a variation of SQL that was more object-centric. Is EQL up to the task? Additionally, depending on the app server you're using, there may be proprietary approaches available to you. As I understand it, JBoss integrates very nicely with Hibernate -- and I seem to recall reading that Hibernate is set to become the officially sanctioned persistence framework for EJB 3.0. I have to wonder however, if using EJB is really the right course of action for your project. EJB is not a tool for beginners, and the areas where it can be usefully applied are far narrower and harder to identify than the Sun hype machine would lead you to believe. It's not a panacea, or a general purpose solution no matter how much it may resemble one. Perhaps your needs would be better served by ditching EJB and just using a more general persistence framework by itself? -JF > -----Original Message----- > From: Boyd E. Hemphill [mailto:[EMAIL PROTECTED] > Sent: Wednesday, June 09, 2004 5:14 PM > To: [EMAIL PROTECTED] > Subject: EJB - Entity Beans > > All: > > First let me say I know only the most basic of Java stuff. > > I am working with a Java colleague on the development of a data model > (MySQL of course :-) and we seem to run into the problem an > Entity Beans > cannot support joins. Can anyone tell me if this is true (If so, what > use are they for any sort of complex data model?). If no, > can you send > me some information on how to implement a join with the Beans and some > possible resources to consult? > > My naïveté leads me to believe I should be able to create a > container of > beans that is the result of any query I can write against the DB. Or > something like this anyway! > > Please help! > > Thanks for your time. > > Best Regards, > Boyd E. Hemphill > [EMAIL PROTECTED] > Triand, Inc. > www.triand.com > O: (512) 248-2287 > M: (713) 252-4688 > -----Original Message----- > From: Sudip Shekhawat [mailto:[EMAIL PROTECTED] > Sent: Wednesday, June 09, 2004 2:33 PM > To: [EMAIL PROTECTED] > Subject: Foreign Key on text field > > Hi, > > I am using MySQL 4.0.17. When I try to create a foreign key on a field > of > the type text, I get this error: > > 040609 15:02:31 Error in foreign key constraint of table > db_name/tb_name: > There is no index in the table db_name/tb_name where the > columns appear > as the first columns. Constraint: > FOREIGN KEY (CEA_key) REFERENCES relation (CEA_key) ON DELETE CASCADE > )TYPE=InnoDB; > > > Can I create a foreign key on the text field?? In the parent > table the > parent column has a index of length 64. > > Thanks > Sudip > > _________________________________________________________________ > Looking to buy a house? Get informed with the Home Buying > Guide from MSN > > House & Home. http://coldwellbanker.msn.com/ > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/[EMAIL PROTECTED] > > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/[EMAIL PROTECTED] > > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
