Re: confused by behavior of 1:n relationship

[Jakob Braeuchi]

hi bonnie,

Bonnie MacKellar wrote:

Sure, I understand that the customer returned in my
first set of code is a proxy. But I thought that
when I traverse the link, the entire object is retrieved.
that's true ojb materialized the real object behind the proxy but the 
payer still references the proxy.

It certainly behaves that way. I can print out
the name of the customer (part of the full business
object) as can be seen from the code. I can also
print out the correct customer ID. So why can't OJB
take that same customerID value and stuff it in
the generated INSERT query? That is what I don't get.
it may be a bug :(

I did not try using a non-proxied reference, but
I bet it would work. I am trying to understand why.
thanks,
Bonnie
 

hth

jakob

 

-----Original Message-----
From: Jakob Braeuchi [mailto:[EMAIL PROTECTED]
Sent: Monday, June 16, 2003 4:46 PM
To: OJB Users List
Subject: Re: confused by behavior of 1:n relationship
hi bonnie,

Bonnie MacKellar wrote:

   

On Friday, I posted asking about a strange bug in my system. 
     

I never got any
   

responses, but I did find the cause of the bug. The problem 
     

is, I don't
   

understand the cause. I was hoping that someone who knows more about
relationship and proxy behavior might enlighten me. I really need to
understand this so I can not make these mistakes in the future.
I have three classes : User, Customer, and PaymentTxn. At 
     

the point at
   

which the strange behavior occurred, I had retrieved a user, using a
criteria query, and was creating a PaymentTxn object. The User object
has a reference to a Customer object, which I wanted to use
in my new PaymentTxn object. The User object's reference was 
specified in the repository_user.xml file like this :
    <field-descriptor
       name="customerID"
       column="customerID"
       jdbc-type="INTEGER"
    />    
    <reference-descriptor
    	  name="customer"
    	  
     

class-ref="com.mobius.activebill.persistentobjects.Customer"
   

          proxy="true"
        >
     

have you tried to use a non-proxied reference-descriptor ?

   

        <foreignkey field-ref="customerID"/>
    </reference-descriptor>
The reference in the PaymentTxn object is specified in the same way.

When I tried to get the Customer via the User object by following the
reference, the strange behavior occurred. I could get the 
     

Customer object,
   

and print out its id properly. But when I tried to add it to the User
object,
the generated SQL got the customer id value wrong. When I changed
the code so that I used a criteria based query to retrieve the
Customer object, the generated SQL was fine. Why? What is 
     

the difference
   

in behavior? The sequence of retrievals looks the same in 
     

either case.
   

Here is the code that did not work :
CustomerInterface customer = payer.getCustomer();
System.out.println("customer name is " + customer.getName());
System.out.println("customer id is " + customer.getID());
paymentTxn.setIssuingCustomer(customer);                 
broker.store(paymentTxn);
The name and id printed out correctly, but after calling 
     

setIssuingCustomer,
   

the associated SQL insert statement had the wrong value (a 0) for
customerID.
     

the customer referenced by payer.getCustomer is actually a proxy !

   

But this code did work :
CustomerInterface customer = 
     

retrieveCustomerByName("TheBigCustomer");
   

System.out.println("customer name is " + customer.getName());
System.out.println("customer id is " + customer.getID());
paymentTxn.setIssuingCustomer(customer);
broker.store(paymentTxn);
     

here the customer is a "real" business object (i assume you did not 
define proxy=true in the class-descriptor)

   

The only difference is the way in which I obtained
the customer. Why should this be different?
thanks,
Bonnie MacKellar
software engineer
Mobius Management Systems, Inc.
[EMAIL PROTECTED]
           

     

hth

jakob

   



     

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