equals/hash code problems

myabar · **Joined:** Tue Apr 29, 2008 6:12 am **Posts:** 3

In my application all the objects stored in the database have an integer code. I've developed the following functions:

Code:

@Override
   public int hashCode() {
      //This method has been reimplemented because of Hibernate. See Hibernate tutorials for more info.
      
      final int prime = 31;
      int result = 1;
      result = prime * result + code;
      // This is done to make the same as the equals method
      if (code == 0)
         result = prime * result + super.hashCode();
      else
         result = prime * result;
      return result;
   }

   @Override
   public boolean equals(Object obj) {
      //This method has been reimplemented because of Hibernate. See Hibernate tutorials for more info.      
      
      if (this == obj)
         return true;
      if (obj == null)
         return false;
      if (getClass() != obj.getClass())
         return false;
      final BusinessObject other = (BusinessObject) obj;
      // the following is done in order to use objects which have not been
      // stored yet to the db.
      if (code == 0) {
         if (other.code != 0)
            return false;
         super.equals(obj);
      }
      if (code != other.code)
         return false;
      return true;
   }

With this functions I say that two objects are equal if the code is equal, or, in case there is no code, that they are the same instance.

When I use this code my application does not work properly. Anyone has any ideas?

Thanks

sagimann · **Joined:** Sun Jun 11, 2006 10:41 am **Posts:** 164

"My application does not work properly" doesn't cut it, sorry :-)
what is your test code, what is the output, what are the exceptions, what hibernate are you using, what dbms????

elch78 · **Joined:** Fri Apr 25, 2008 5:09 am **Posts:** 4

I have the same problem at the moment.

The problem may be

Code:

if (getClass() != obj.getClass())
         return false;

obj.getClass returns the proxy class which is not equal to the persistent class. You can get the actual class with HibernateProxyHelper.getClassWithoutInitializingProxy(obj) but I´d like my business tier code to be free of any hibernate specific code ...

Cameron McKenzie · **Posted:** Tue May 27, 2008 10:12 am

It definitely looks like you're doing a comparison on the proxy. This will not give you the desired behaviour.

elch78 · **Joined:** Fri Apr 25, 2008 5:09 am **Posts:** 4

How can I compare with the object behind the proxy?

Edit:
Wrong question, I´ve given the answer for this myself. What I wanted to know was how to get the Object behind the proxy. My Problem ist that the test for object identity in the equals method fails because the object is compared with its proxy.

Code:

   public boolean equals(Object obj) {
      if (this == obj)
         return true;
      ...
   }

minadaoud · **Joined:** Wed May 28, 2008 6:06 am **Posts:** 6

elch78 wrote:

How can I compare with the object behind the proxy?

Code:

   public boolean equals(Object obj) {
      if (this == obj)
         return true;
      ...
   }

i think the error here is using the ( ==) it checks if the reference of the objects are the same or not.

Cameron McKenzie · **Posted:** Mon Jun 09, 2008 9:37 am

== is simply comparing the memory locations of two objects. If they are on different JVMs, they will have a different == result, even if they represent the same row of data in the database.

Use .equals in your comparisons.

This tutorial discusses the requirements and why we need to override .equals and hashcode in a JPA or Hibernate entity. It uses the compound primary key class as a backdrop, but it applies for all entity based classes you will run into:

http://jpa.ezhibernate.com/Javacode/learn.jsp?tutorial=15usingcompoundprimarykeys