In EJB 1.1 spec, it seems that environment variables are shared by instances
with same home, but not shared by other beans.... Does this mean that bean
provider can create the environment variable with same name for every ejbs?
For example, Can I have three different entity beans with same env-name, but
their values are different?? and, can I expect that each bean instance grab
only the environment variables that are avaible to it? Any help is
appreciated.
Se Hee
-->-----Original Message-----
-->From: A mailing list for Enterprise JavaBeans development
-->[mailto:[EMAIL PROTECTED]]On Behalf Of Al Fogleson
-->Sent: Tuesday, May 16, 2000 11:38 AM
-->To: [EMAIL PROTECTED]
-->Subject: Re: Object-relational problem
-->
-->
-->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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