Nothing says that the address has to be an EJB. :)
You could make the address a class and have it grab all the addresses from
the database, then in the customer bean you can match the address with the
customer using the PK and FK relationship. if you further implement the
address class as a singleton it can retain the result set over multiple
instances of the Entity bean. In your case I would likely use a
findAllCustomers, and spit that back to the rendering engine to put on the
web page. makes for 2 database calls, one to get all the customers, and one
to fill the address class.
Al
----- Original Message -----
From: Tim Fox <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, May 18, 2000 11:17 AM
Subject: Object-relational problem
Here's a problem I've been chewing over for a while now and haven't come
up with a satisfactory solution.
It's one of the classic object-relational problems.
Here's a simplified description (please note that this is a fictitious
example - I've simplified it for clarity)
I have 2 ejbs: a Customer and an Address.
The customer has a home address.
I'm displaying a list of all customers satisfying certain criteria along
with their home address on a web-page.
There would be one customer & address per line.
This would look something like:
Customer Name Customer Address
=========== =============
Joe Bloggs 1 High Street, Newtown
John Doe 23 Synchronicity drive, London
Jane Doe 2 Big Street, Badville
Now the page is hit a lot so I want to get the entire list using one
query - this is pretty easy in SQL - a simple join across the customer
and address tables.
The last thing I want to do is query for all the customers, then, for
each customer query for the address - this would cripple the system
since I'd have a new query for each row of the page.
However, if I'm using ejb then it seems I could either:
1.
Use a finder method to get the list of customers given the criteria,
then...
For each customer in the list, use the findByPrimaryKey() (or whatever)
method to find the address.
This is probably the worst solution since it would probably involve a db
query for each customer address.
2.
Use a finder method to get the list of customers given the criteria,
then...
Use a finder method to get the list of addresses given the criteria.
This basically involves running the same (or very similar) query twice -
once in the Customer finder method, and once in the Address finder
method.
This, although better than 1) seems very wasteful
3.
Do the query once, and pass the resultset into the finder methods of the
customer and address objects - don't know if this is possible though due
to remote calls and marshalling of the resultset
4. Create a denormalised ejb called AddressCustomer which is an
amalgamation of the Address and Customer objects. Yuck!!!
Then I also end up with an AccountCustomer, AccountCustomerStatement,
ProductManufacturerSupplier etc. ad infinitum objects.
Basically the nice OO model gets shot to f*** !!
I'd been interested in any comments/solutions people have implemented,
as this is really bugging me
(BTW if I wasn't using ejb I'd use 3) since I wouldn't have any remote
calls problems).
Cheers
--
Tim Fox (��o)
Senior developer
Hyperlink plc
http://hyperlink.com
email: [EMAIL PROTECTED]
phone: +44 (0) 207 240 8121
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