From: Date: June 10 2004 3:38am
Subject: RE: EJB - Entity Beans
List-Archive: http://lists.mysql.com/mysql/167026
Message-Id: <200406100136.i5A1aZ2S023484@smvcsa01.yfdirect.net>
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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Therefore, some of what I say may be a bit out of date.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:bhemphill@stripped]=20
> Sent: Wednesday, June 09, 2004 5:14 PM
> To: mysql@stripped
> Subject: EJB - Entity Beans
>=20
> All:
>=20
> First let me say I know only the most basic of Java stuff.
>=20
> 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=20
> 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,=20
> can you send
> me some information on how to implement a join with the Beans and some
> possible resources to consult?
>=20
> My na=EFvet=E9 leads me to believe I should be able to create a=20
> container of
> beans that is the result of any query I can write against the DB.  Or
> something like this anyway!
>=20
> Please help!
>=20
> Thanks for your time.
>=20
> Best Regards,
> Boyd E. Hemphill
> bhemphill@stripped
> Triand, Inc.
> www.triand.com
> O:  (512) 248-2287
> M:  (713) 252-4688
> -----Original Message-----
> From: Sudip Shekhawat [mailto:sudip_s_s@stripped]=20
> Sent: Wednesday, June 09, 2004 2:33 PM
> To: mysql@stripped
> Subject: Foreign Key on text field
>=20
> Hi,
>=20
> I am using MySQL 4.0.17. When I try to create a foreign key on a field
> of=20
> the type text, I get this error:
>=20
> 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=20
> columns appear
> as the first columns. Constraint:
> FOREIGN KEY (CEA_key) REFERENCES relation (CEA_key) ON DELETE CASCADE
> )TYPE=3DInnoDB;
>=20
>=20
> Can I create a foreign key on the text field?? In the parent=20
> table the=20
> parent column has a index of length 64.
>=20
> Thanks
> Sudip
>=20
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