confused by behavior of 1:n relationship

[Bonnie MacKellar <BM...@mobius.com>]

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"
      	>
      	<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.

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);

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.
bmackell@mobius.com

             

Re: confused by behavior of 1:n relationship

[Jakob Braeuchi <jb...@gmx.ch>]

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.
>bmackell@mobius.com
>
>             
>
hth

jakob

>
>  
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