Question

I’m wondering how to write a correct equals() and hashCode() for Hibernate Entities which have a Lazy Loaded ManyToOne relation to another Entity which is important as a business key. Note, that I already read the Hibernate documentation on this topic and I know I must/should not use the object id.

To clarify, here an example:

public class BusinessEntity implements Serializable
{
    //for simplicity, here just the important part
    private String s;

    @ManyToOne(fetch= FetchType.LAZY )
    private ImportantEntity anotherEntity;

    @Override
    public boolean equals( Object obj )
    {
       //Here I would like to call something like
       // (obj.getAnotherEntity.getName.equals(getAnotherEntity.getName) && obj.getS().equals(getS());

       return true;
    }
}

Of course this is just a simplified example. But I hope I could explain my scenario. Has someone tried something like that before? I did not find anything regarding to this topic.

Answer 1

For simplicity I have skipped null-safety code. But the idea is to create
additional property which will persist entity name and will not expose it to the outside world

public class BusinessEntity implements Serializable
{
    //for simplicity, here just the important part
    private String s;

    @ManyToOne(fetch= FetchType.LAZY )
    private ImportantEntity anotherEntity;

    private String anotherEntityName;

    @Override
    public boolean equals( Object obj )
    {
        if(BusinessEntity.class.isAssignableFrom(obj.getClasS())){  
         BusinessEntity other =  (BusinessEntity)obj;
         return other.anotherEntityName.
                equals(this.anotherEntityName) && 
                other.s.equals(this.s);

        }
       return true;
    }
    public void setAnotherEntity(ImportantEntity ie){
        anotherEntityName= ie.getName();
        anotherEntity = ie;
    }
}