Pet store architecture question
Hello,
I have downloaded Sun's sample J2EE pet store
enterprise application 1.1.2. I was surprised
to find that in at least two entity beans that
they loaded model data into the entity bean
in the ejbFindByPrimaryKey method:
AccountEJB.java:
.
.
public String ejbFindByPrimaryKey (String key) throws FinderException {
try{
AccountDAO dao = getDAO();
String userId = dao.findByPrimaryKey(key);
this.accountDetails = dao.load(userId);
return(userId);
.
.
Could someone please tell me if there is any
benefit to using the DAO to load data in the ejb
find method? Why not just load the data in
the ejb load method? Is this even a good idea?
Thanks for any advice!
[800 byte] By [
neu9109] at [2007-9-26 5:19:19]
Thank you for your responses.
I think I might have phrased my question poorly,
and that's why I think I received the feedback
I did.
I wasn't questioning the use of DAO. As a pattern,
I see how useful it is. What I was surprised about
was WHERE the DAO.load method was used.
Why should the entity bean read data from the DAO
in the ejbFindByPrimaryKey method? If I was
writing the code, I would leave out the line:
this.accountDetails = dao.load(userId);
because that's the job of the ejbLoad method. Since
loading from the DAO can potentially be slow, doesn't
this lead to a slight performance problem?
Thanks for your reply!
I thought the way it worked was:
1) A client calls AccountHome.findByPrimaryKey
2) The container calls AccountEJB.ejbFindByPrimaryKey
which returns a PK
3) The container sets the PK into the EntityContext
of an EJBObject
4) The container calls the ejbLoad of the EJBObject.
This EJBObject calls getPrimaryKey of its
EntityContext and uses its DAO to load the
account data
5) The container returns a remote interface to the
EJBObject to the client
6) The client calls getDetails of the remote interface
If this logic is correct, then according to the
pet store code, account data is loaded after the
container calls ejbFindByPrimaryKey AND after ejbLoad.
So it seems wasteful to load the data twice. I don't
see how you can avoid the ejbLoad in this scenario...
I don't think ejbFindByPrimaryKey(PK) will result in ejbLoad() being executed on the EntityBean.
After u send ejbFBPK(PK), u get the RI for the EB.
Then, when u send u'r very first busines method to the RI (tx/non-tx), then the container would always invoke the ejbLoad() method on the EB.
Thereafter, every transactional business method would result in a ejbLoad(), business method, ejbStore() on the EB.
For non-transactional business methods, u can never be sure that ejbLoad() will be called....
