This actually has to do with the use of Hibernate Contextual Sessions ( the
thread-bound session returned by getCurrentSession() ), not Hibernate's
behavior when using JDBC transaction semantics.
http://www.hibernate.org/hib_docs/v3/reference/en/html/architecture.html#architecture-current-session
We might want to consider using the ManagedSessionContext for this and
managing the session binding/opening/closing ourselves; that might be
cleaner and more localized than trying to manage flush() ourselves.
The problem with managing flush() explicitly is that it tends to lead to
having to assume boundaries in composition of operations (where the flush()
is called). For example, if you query as part of a method you have to flush
or know that flush is not necessary.
Also, looking back at the initial message, I was confused by the phrase "2)
enabling lazy fetching on all objects and
associations" in Allen's message. Did you mean all single and
collection-valued associations? I don't think lazy fetching of object
properties will be a win at all.
We might also consider using join fetching for certain associations,
particularly around weblog entry data. Maybe you looked at this already?
--a.
----- Original Message -----
From: "Allen Gilliland" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Tuesday, November 14, 2006 11:16 AM
Subject: Re: Business layer cleanup for 3.2
Craig L Russell wrote:
On Nov 14, 2006, at 9:48 AM, Allen Gilliland wrote:
It's not unlikely that we will break some things temporarily and not
notice it for a while. The riskiest aspect to me in this regard is
lazy fetching because it really demands that the session span the
entire request, which we seemed to have a hard time doing properly
earlier, and I'm not sure exactly why. We backed out of lazy fetching
just before one release a ways back because we would hit odd session
closed exceptions that we didn't have time to figure out. It's
possible that some of Allen's earlier session management cleanups
already got us out of those issues. It's a good idea to revisit this
now. I think that is also likely to make us more portable to
optimizations in other persistence implementations that expect
essentially the same session management pattern.
so far I have been able to make all the changes that I think are correct
and I have all the unit tests running correctly, so what I am doing now
is going over the actual webapp and running through all the operations
that I can to find and fix anything that I find. Things are definitely
cropping up, but so far the lazy initialization problem hasn't come up.
The bigger problem has been caused by changing the hibernate config to
use FlushMode.NEVER, which means that hibernate doesn't flush its state
to the db until we explicitly call the flush() method on the Session. As
it turns out, a *lot* of the stuff we were doing has been very reliant
on auto flushing for it to work, so there have been a handful of places
where I have had to figure out how to fix that problem. So far so good
though, and I hope to have things cleaned up enough to commit in the
next day or so.
What is the reason you want to set hibernate config to use
FlushMode.NEVER? From what I know of it, this is an antipattern.
I will do some more reading about it because if it is an antipattern then
I should reconsider it, but the main reason why I am trying this now is to
get around some of Hibernates automation. The main problem being that
Hibernate's default handling for JDBCTransactions is setup such that
whenever you commit a transaction it closes the Session that was handling
that transaction, and that causes a problem with lazy initialization
because objects can no longer access associations if the Session they were
attached to is closed. I sifted through things on the Hibernate forums to
find other folks with the same problem and how they fixed it and that's
where I came up with FlushMode.NEVER.
It may be possible that we can accomplish that without using
FlushMode.NEVER, but i'll have to look at it more carefully to see.
Regardless of whether or not we use it I still think that in principal it
should work. The places where I have found things broken by this change
is situations where we are kind of circumventing our object model and
going directly to the db which causes a slight disconnect. i.e. if I call
saveObject(foo) and then later in the same transaction try to
getObject(foo) via a query before it has been flushed to the db. So far
these scenarios look more like slightly incorrect code as much as anything
else, but I am still investigating.
I'll look into this more today though.
-- Allen
Craig
-- Allen
--a.
----- Original Message ----- From: "Allen Gilliland"
<[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Monday, November 13, 2006 4:46 PM
Subject: Re: Business layer cleanup for 3.2
certainly. I didn't do much in the way of renaming things yet, the
first pass was mainly about fixing up the Hibernate config to work the
way I think it should have been working and clearing out some things
along the way. Once that is done then I plan to go over the business
layer more times and find places where methods should be renamed,
removed, or consolidated in any way. I also want to keep building on
the unit tests because I think they are pretty good now, but there are
a few gaps here and there.
At the end of the day this work will definitely help to make the work
on the JDO/JPA backends quite a bit easier.
-- Allen
Craig L Russell wrote:
Hi Allen,
We had discussed a number of issues with the manager classes such as
misspelled method names and incomplete functionality (having the
caller iterate through collections).
I'd be happy to review what you've done in terms of cleanup.
Regards,
Craig
On Nov 13, 2006, at 2:10 PM, Allen Gilliland wrote:
One of the things that I am planning to do for the 3.2 release is do
some audit/cleanup of the current business layer code. There are a
variety of things which could use improving, but the main goal is to
fix our Hibernate configuration so that we are 1) properly using the
open session in view pattern and 2) enabling lazy fetching on all
objects and associations.
Right now our Hibernate config is pretty messy and doesn't take
advantage of many of Hibernate's performance features, so the main
reason to do this work is to improve the performance of the business
layer. The second big reason is just to reduce clutter and simplify
the code as much as possible. There are plenty of places in the
code where we have methods that aren't used at all or methods which
are duplicated, so those would all be cleaned up.
I have most of this work done already (but not checked in) and there
aren't really any surprise changes that I had to make except when it
came to the hierarchical objects. I tried for multiple days to get
the hierarchical objects to work with the updated hibernate config
and the current data model, but I kept running into problems. So to
fix the problem I had to make a small tweak to the way hierarchical
objects are persisted which fixed my issues and I believe
drastically simplifies the problem overall. The basic change is
that I have completely removed the HierarchicalPersistentObject
class and Assoc and it's subclasses and changed the data model so
that we have a more normal hierarchical model.
So, for weblog categories I added a simple 'parentid' column to the
weblogcategory table and that allows a category to manage
relationships between it's parent and children directly. Same goes
for the FolderData class, but as it turns out that column already
existed in the schema but wasn't being used. Upgrade path for both
of these is fairly simple and only requires populating these columns
with the right value.
I'm not sure if anyone really wants to see more of a proposal for
this, which is why I started with an adhoc description here on the
list. As I said, I am not actually modifying anything from a
feature point of view, only cleaning up what is already there. If
anyone wants to see more about the changes to the hierarchical
objects then I can post them on the wiki or something.
-- Allen
Craig Russell
Architect, Sun Java Enterprise System
http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!
