CMP Entity Beans Vs BMP Entity Beans

[Asuthosh Borikar]

When is it appropriate(rather, the only choice) to use a BMP Entity Bean as against a CMP Entity Bean? We have a table which also has a child table. For each row in the parent table, there will be one or more rows in the child table. If I want to develop an entity Bean for the parent table, can I use a CMP Bean? Is it possible to depict this relation correctly, using the Deployment Descriptors, according to EJB1.1? Please help. Thanks!

[Jim Baiter]

If you have more than one table involved you need to use BMP
or if your database supports updateable views you could use
CMP and create a view to reference.

[Asuthosh Borikar]

Thanks Jim. That's what I thought, but wanted to confirm my thoughts.

[svoropay]

It is a common misconception to think that CMP is limited to only one-table database schemas. Yes, with CMP you can map your bean to only one database table/view, but doesn't necessarily mean that you are limited to one-table schemas.

[Matt Midcap]

svoropay,
The Java Ranch has thousands of visitors every week, many with surprisingly similar names. To avoid confusion we have a naming convention, described at http://www.javaranch.com/name.jsp . We require names to have at least two words, separated by a space, and strongly recommend that you use your full real name. Please choose a new name which meets the requirements.
Thanks,
Matt

[Michael Hildner]

Dear svoropay,
Would you please provide and example or online resource that explains how to use CMP with more that one table?
Thank you,
Michael

[Sergei Voropay]

It is hard to come up with any good online resource on this topic, but a very good printed resource would be "Enterprise Java Beans 2d Ed." by Richard Monson-Haefel. A whole section called "Entity beans relationships" in chapter 9 is devoted to this topic, where the author suggests a few possible ways of dealing with relationships between EJBs.
Regards,
Sergei

[Asuthosh Borikar]

Sergie,
I've read that topic from Richard's book. He does specify the CMP way of dealing with relationships between EJBs, but he also states that UNLESS your App.Server supports Object-to-Relational data mapping, the only way of dealing with many-to-one relationships is to use BMP. I just wanted to make sure that this issue is cleared out, and that I've understood that book correctly. Your comments are welcome. Thanks!

[Sergei Voropay]

It looks like people have mixed opinions on this topic. Some say it is ok to mimic one-to-many relationships with CMP ejbs through bean references, some say that it's too costly and inefficient in terms of performance and alternative solutions (o/r mapping) should be used. I'm a supporter of the former approach considering the benefits CMP provides even if I have to sacrifice some performance. For small to medium complexity database schemas involving one-to-many relationships, mimicking the relationships between beans through references is very easy -- just extend the concept provided in the book to collections of objects. Here is a little example on one-to-many relationships between CMP ejbs from the Borland web site: http://www.borland.com/techpubs/books/appserver/appserver40/examples/ejb/pigs/README.html.

[sarah00]

Sergei,
That web site is not exist anymore, do you know the
correct one?
Thanks a lot,
Sarah

[Matt Midcap]

Hi "sarah00",
The Java Ranch has thousands of visitors every week, many with surprisingly similar names. To avoid confusion we have a naming convention, described at http://www.javaranch.com/name.jsp .
We require names to have at least two words, separated by a space, and strongly recommend that you use your full real name. Please choose a new name which meets the requirements.
Thanks.

[George Toronto]

http://www.borland.com/techpubs/books/appserver/appserver40/examples/ejb/pigs/README. html
But this sample is not object of the discussion, right?
[This message has been edited by George Toronto (edited March 04, 2001).]