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Struts & Hibernate
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| | | DAO relation with business object | DAO relation with business object 2004-06-22 - By Soumen Saha
Back
Hi Wim,
The best way to diffrentiate is to understand that Business Objects
reflect the Object Model of your system. It should not
be what your database object look like and neither what the UI want. for UI,
you need to use Value Objects.
So your dataaccess layers returns a Business Object or a hierarchy of
Business Objects to the Business Layer. which in turn
does required business rule implementation and returns the modified
BusinessObject to the UI Layer. The UI helpers convert
the Business Object to Value Object for UI display purposes
2nd Problem:
Your DAO is part of the dataAccess Layer so it should return a
BusinessObject.
So public User getUser(int id); should be your signature.
- Somu.
-- -- Original Message -- --
From: "Sullivan, Sean C - MWT" <Sullivan.Sean@(protected)>
To: <J2EEPATTERNS-INTEREST@(protected)>
Sent: Monday, June 21, 2004 9:34 PM
Subject: Re: DAO relation with business object
These resources may be helpful:
http://corej2eepatterns.com/Patterns2ndEd/DataAccessObject.htm
http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObjec
t.html
http://daoexamples.sourceforge.net/related.html
http://www-106 (See http://www-106.ora-code.com).ibm.com/developerworks/java/library/j-dao/
-- --Original Message-- --
From: An interest list for Sun Java Center J2EE Pattern Catalog
[mailto:J2EEPATTERNS-INTEREST@(protected)] On Behalf Of Deblauwe, Wim
Sent: Monday, June 21, 2004 8:09 AM
To: J2EEPATTERNS-INTEREST@(protected)
Subject: DAO relation with business object
I've looking at the DAO pattern lately and have some problems with it.
Especially what is ment by Business Object and ValueObject?
In my words I would call a class User that is a POJO a Business Object,
and I would place it in a package "business".
I would then have a class ValueUser in my data package that has all the
same methods as business.User. In fact, business.User is just a delegate
to data.ValueUser.
Is this already correct? Or is the business class something else and is
my User class already a ValueObject?
2nd problem:
When I then create my DAO, e.g. UserDAO. This would typically reside in
the data package. There are 2 options then:
public User getUser(int id);
or
public ValueUser getUser(id);
If my business.User class is already a ValueObject, then a class from my
data-layer is dependant on a class from my business-layer. This would be
undesirable I think.
Otherwise we refer to the ValueUser which is in the same layer, so this
seems ok. But when you try to unit-test User when it is just a delegate
for ValueUser, you will do this:
ValueUser valueUser = new ValueUser();
valueUser.setName( "testName" );
... some more here
User user = new User();
user.setValueObject( valueUser );
assertEquals( user.getName(), "testName" );
And I really don't like this. You have to create 2 objects, where 1
should be enough.
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