RE: DAO design pattern -- JAVA400-L

Niall,

We are not using stored procedures as DAO layer, but calling stored
procedures to access our existing business logic on the 400. 

Hibernate 2 gives you no way to do this. 
Hibernate 3 allegedly does but I tried it and it does not work.

Tried custom persisters, but decided that it would be too complex, and take
too long. 

How did you get your lazy loading to work. Looking at it seemed to indicate
you would have to keep sessions open, or reattach to new sessions, as when I
tried it the application would crash if the original session was not
available?

Trust me, Ive crawled the forums extensively, and a lot of the problems I
solved were as a result of searching the forums.

Don't want this to saound like im knocking hibernate, it's a great
framework. I just don't think its finished. I found I had to put in a great
deal of work in to get it to do what I wanted.

Comparing my experience of Hibernate to Ibatis, 
Ibatis is not as powerful, but it works straight out of the box. 

I have had very few problems getting Ibatis to do what I want, and where I
got stuck, it seemed to be easy to find workarounds.

cheers
Colin.W

http://as400blog.blogspot.com
 
Extension   5800
Direct dial   0870 429 5800


-----Original Message-----
From: Niall.Smart@xxxxxxxxxxxxxxx [mailto:Niall.Smart@xxxxxxxxxxxxxxx] 
Sent: 04 January 2005 12:16
To: Java Programming on and around the iSeries / AS400
Cc: 'Java Programming on and around the iSeries / AS400';
java400-l-bounces@xxxxxxxxxxxx
Subject: RE: DAO design pattern


Colin

Fortunately I have not needed to work with stored procedures much.  If you 
are using stored procedures as a kind of DAO layer then Hibernate probably 
won't be of much use, it doesn't really fit that model.  It would be worth 
looking into extending it by through custom persisters for your classes 
which call the stored procedures. 

We use a few PL/SQL functions which perform some data-intensive 
calculations.  Using these isn't a problem, you can either hide them 
behind a view and map the calculated column as read only, or else use a 
property with a formula expression instead of a column reference.

I've also heard Hibernate 3 will have include more support for stored 
procedures.

Lazy loading is working ok for us here, but we are still figuring out the 
various cache strategies and levels.  As Hibernate is quite complex, I've 
found that at first it doesn't do what you expect, but then after a bit of 
experimentation you understand the subtleties and then find it works as 
described.

As regards the forum -- it is hit and miss, there is a lot of good 
material in the archives through its worth searching there first (use AND 
instead of OR, otherwise the search results are close to useless).   The 
book by the authors of Hibernate called "Hibernate in Action" is out now 
-- worth checking out.   I have found that they are ruthless in to closing 
bugs as WONTFIX or WORKSFORME!

Niall




Colin Williams <colin.williams@xxxxxxxxxxxx> 
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04/01/2005 12:00
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RE: DAO design pattern






Niall,

How much joy have you had with hibernate. I have had a lot of problems
getting it to do some stuff, especially stored procedures.

For stored procedures I had to drop back to native SQL. I soon as I had to
do that I lost the benefits of using hibernate in the first place.

Apparently you can access stored procedures in the latest version, tried 
it,
didn't work.

The other thing that I found was that hibernates lazy loading is either a)
very complex to setup, or b) just plain does not work, and I spent
considerable time trying to get it to work.

With these and other problems I gave up and switched to Ibatis. It was
sooooo much easier, as you have control of the sql.

The thing that put the nail in the hibernate coffin for me, is that when I
had problems I posted questions on the hibernate forum. My questions were
ignored?

cheers
Colin.W

http://as400blog.blogspot.com
 
Extension   5800
Direct dial   0870 429 5800


-----Original Message-----
From: Niall.Smart@xxxxxxxxxxxxxxx [mailto:Niall.Smart@xxxxxxxxxxxxxxx] 
Sent: 04 January 2005 11:23
To: Java Programming on and around the iSeries / AS400
Cc: 'Java Programming on and around the iSeries / AS400';
java400-l-bounces@xxxxxxxxxxxx
Subject: RE: DAO design pattern


We use Hibernate here, it is extremely useful indeed.

Anyone want to elaborate on the pros and cons of JDBC versus AS400File?




Colin Williams <colin.williams@xxxxxxxxxxxx> 
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Lim, Niall,

And if you want to take this stuff even further,

Use a framework such as Ibatis or Hibernate for your Object/Database
mapping.

Hard work initially, especially hibernate, but as your application gets
complex, you do see the benefits

cheers
Colin.W

http://as400blog.blogspot.com
 
Extension   5800
Direct dial   0870 429 5800


-----Original Message-----
From: Niall.Smart@xxxxxxxxxxxxxxx [mailto:Niall.Smart@xxxxxxxxxxxxxxx] 
Sent: 04 January 2005 10:59
To: Java Programming on and around the iSeries / AS400
Cc: java400-l-bounces+niall.smart=friendsfirst.ie@xxxxxxxxxxxx; Java
Programming on and around the iSeries / AS400
Subject: Re: DAO design pattern


Lim

Create an interface which defines the data related operations 
independantly of any particular representation/access method (i.e., 
file/JDBC, etc)

public interface SomeObjectDAO {

        public void create(SomeObject object)
                throws DAOException;

        public void delete(Integer objectID)
                throws DAOException;

        public SomeObject findByID(Integer objectID)
                throws DAOException;

        public List findByKeyword(String keyword)
                throws DAOException;
}

Then write an implementation of this interface using the JT/400 API:

public class JT400SomeObjectDAO {

        public SomeObject findByID(Integer objectID) {
 
                AS400File file = ....

                SomeObject someObject = new someObject();

                someObject.setFoo(file.readInteger());
 
                return someObject;
        }

        // ...
}

And finally write a factory to create instances of SomeObjectDAO:

public class SomeObjectDAOFactory {

        private static instance = new SomeObjectDAOFactory();

        public static SomeObjectDAOFactory getInstance() {
                return instance;
        }

        public SomeObjectDAO newInstance() {
                return new JT400SomeObjectDAO();
        }

}

You don't gave to use checked exceptions.   A framework like spring can 
obviate the need for trivial factory objects.




"Lim Hock-Chai" <Lim.Hock-Chai@xxxxxxxxxxxxxxx> 
Sent by: java400-l-bounces+niall.smart=friendsfirst.ie@xxxxxxxxxxxx
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DAO design pattern






Anybody has a good example on how should I design my web application for 
any file access related transaction?
 
I'm using struts to create this web apps.  I just wonder when I'm in the 
Action Form and I need to do some edit/insert/update on a record in a 
file, what is the correct way to design this.  I've read some article 
about DAO design pattern.  If this is a good approach, can anybody provide 


some example.  (Note: I'm using Tomcat4.1 and plan to use DBCP for 
connection pooling.) 
 
thanks.
-- 
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