Ejbload() on CMP with transaction = supports - why called before every method?

Question

If an entity bean (CMP v2) has its transaction attrib "supports", why
when a client (ejb/servlet/jsp) calls its business methods does WLS
call ejbLoad() before every method call? Note that the calls do not
occur inside a transaction!
This is not intuitive to me. I would think that ejbLoad() would be
called once when the bean is activated and then all business methods would
access that data.
Note that if you put the entity bean behind a session bean with a
transaction attrib "Required", then the ejbLoad() gets called once no
matter how many business methods are called from the session bean.
This is (obivously) correct.
Why is this relevant? The latest java petstore demo essentially calls
EJBLocal's from jsp (via taglib's) - I guess no different from WLS
EJB to taglib product - where the fine grained getter methods are
called. From what I gather, this means that every one of the jsp
get methods results in a database read! This can't be right!
What am I missing? As above, if the entity bean has "supports"
and is called from a jsp, it appears that ejbLoad()/ejbStore()
would be called for every jsp taglib invocation.
Glenn

Answer 1

"Glenn R. Kronschnabl" wrote:
Rob,
Thanks for your reply. This implies that even EJBLocals with fine
grained getter methods should never be used outside a tx scope.Yes, unless you are using Read-Only entity beans which cache data for longer
periods of time.
Even
though you bypass the RMI semantics, you'll be killed by the local tx.
Which to me says that using EJB's from JSP (even via tags) is a bad
idea because each getter method will result in a database read/write,
(unless you go with a readonly EJB as you stated).
Accessing transactional entity beans via tags is probably a bit off. You
could start the tx in the JSP or the tag library, but I don't really like
that pattern much. I prefer making the tags more coarse-grained and having
the tags talk to a stateless session bean which in turn talks to the entity
beans.
>
Unfortunately, I've been seeing some threads on the net advocating
using EJBLocals with tx=supports because one of the most common
patterns has session beans (where you can specify your desired tx)
in front of entity beans (so you're set methods are protected via
the session bean tx),RIght, I think Required or Mandatory is a better choice for the entity beans
here.
but then you can use the EJBLocal (via tags)
on a JSP page (no tx) to view the data via fine grained getter
methods.Other than the performance issues, I dislike this because it exposes the
entity bean directly to the JSP. If I have to go through an interface (the
session bean) to access the entity bean, then I shouldn't have another route
to access the entity bean directly.
-- Rob
>
As you state, this is a disaster because each getter method
will run in a local tx, requiring a database read/write. Oouch!
Glenn
On Thu, 06 Dec 2001 17:08:07 -0600, Rob Woollen wrote:
First off, I wouldn't recommend that you ever run any EJB with the
'supports' transaction attribute. If you want transactional behavior
use Required, RequiresNew, or Mandatory. If you want to run in an
unspecified tx, use NotSupported or Never.
WLS runs entity beans with an unspecified tx in their own local tx.
That's why you see the reads and writes on the method call boundary.
Your scheme of only reading when the bean is activated could make the
bean's data out of sync with the underlying database. That's acceptable
in many cases, and that's why we have the Read-Only entity bean option.
It gives you exactly what you'd like.
-- Rob
"Glenn R. Kronschnabl" wrote:
If an entity bean (CMP v2) has its transaction attrib "supports", why
when a client (ejb/servlet/jsp) calls its business methods does WLS
call ejbLoad() before every method call? Note that the calls do
not occur inside a transaction!
This is not intuitive to me. I would think that ejbLoad() would be
called once when the bean is activated and then all business methods
would access that data.
Note that if you put the entity bean behind a session bean with a
transaction attrib "Required", then the ejbLoad() gets called once no
matter how many business methods are called from the session bean. This
is (obivously) correct.
Why is this relevant? The latest java petstore demo essentially calls
EJBLocal's from jsp (via taglib's) - I guess no different from WLS EJB
to taglib product - where the fine grained getter methods are called.
From what I gather, this means that every one of the jsp get methods
results in a database read! This can't be right! What am I missing? As
above, if the entity bean has "supports" and is called from a jsp, it
appears that ejbLoad()/ejbStore() would be called for every jsp taglib
invocation.
Glenn
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