JPA composite keys problem

[Zaeed McColin]

hi guys, I'm new in JPA
I have a table with composite key in my DB
in related entity bean I use @IdClass annotation for composite keys, (1:is it cool? what's the difference between @IdClass & @EmbeddedId?)

well in composite keys related class I override boolean equals(Object obj) method
but seems I should override int hashcode() method too
i know a little about hashcode

and problem
how do I override this guy?
I mean what is it for?

code for composite keys class

package Jbeans;

import java.io.Serializable;

public class test03pk implements Serializable{
    public int testId;
    public int test3Id;
public test03pk(int testId,int test3Id){
    this.testId=testId;this.test3Id=test3Id;
}
public test03pk(){}
    @Override
public boolean equals(Object obj){
        boolean res=false;
            if(obj==null){res=false;}
            else if(!obj.getClass().equals(this.getClass())){res=false;}
            else{test03pk pk=(test03pk) obj;
            if(this==pk){res=true;}
            else if((Object)this.testId!=null &&(Object)pk.testId!=null && this.testId==pk.testId){
                if((Object)this.test3Id!=null &&(Object)pk.test3Id!=null && this.test3Id==pk.test3Id){
                res=true;
                }
            }else{res=false;}
            }
        return res;
    }

    @Override
    public int hashCode() {
        if((Object)this.test3Id==null||(Object)this.testId==null){return 0;}
        else{return this.test3Id ^ this.testId;}
    }
}

[Devaka Cooray]

what's the difference between @IdClass & @EmbeddedId?

ArAsh,

The @EmbeddedId is used to annotate an ID field of an entity, which has a separate composite class, as below:

@EmbeddedId
protected NameAndAge key;

(Where NameAndAge is a separate class which is annotated with the @Embeddable annotation).

In the above case, you can simply pass an NameAndAge object to set the primary key when it is needed.


The IdClass method is used to include multiple @Id fields to the same entity

@Entity
@IdClass(NameAndAgePK.class)
public class User{
     @Id protected int name;
     @Id protected int age;
}

(Where NameAndAgePK is a POJO class)

In this case, the above POJO class is used to 'evaluate' the primary keys before associating them with the entity.

i know a little about hashcode

and problem
how do I override this guy?
I mean what is it for?

You might know that hashcode is a numerical representation of the identity of an object; hence the business logic of overriding it is dependent on your requirements, and the class specifications.



Note: I feel your business logic for the equals(Object) method is too long. You can implement it as below, in a nice way:

@Override   
public boolean equals(Object obj){
	return (obj instanceof test03pk)&&testId==((test03pk)obj).testId&&test3Id==((test03pk)obj).test3Id ;
}

[Zaeed McColin]

Ba Sepas (thank you) Mr. Cooray
as i understood we use @IdClass annotation when we want for example check some condition, evaluate or something like that in our composite key

well if I put evaluating on DB(MySQL), I mean check the correct and legal record for adding in table
is it necessary to check and evaluating again with JPA again?(I mean use @IdClass for keys)
can I use @EmbeddedId instead of it?

Ba Sepas