hibernateproxyequals

Hibernate equals and proxy

I have one BaseEntity which abstracts id and version property. this class also implements hashcode and equals based on PK (id) property. 

BaseEntity{

    Long id;
    Long version; 

public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((id == null) ? 0 : id.hashCode());
    return result;
}

public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    BaseEntity other = (BaseEntity) obj;
    if (id == null) {
        if (other.id != null)
            return false;
    } else if (!id.equals(other.id))
        return false;
    return true;
}


}

now two Entity A and B extends BaseEntity as below

A extends BaseEntity{
    `B b`
     B getB(){return b;)
     void setB(B b){this.b=b;}
}

B extends BaseEntity{
}

object b1;
object a1;
a1.set(b1);
session.save(a1) //cascade save;

close session load a with lazy b and try a1.getB().equals(b1) gives false but if i compare with a1.getB().getId().equals(b1.getId()) then gives true strange!! i think it is because of java assist proxy object, anyway to resolve this?

Solution

  • To be able to lazy-load the a.b association, Hibernate sets the b field in a to a proxy. The proxy is an instance of a class that extends B, but is not B. So, your equals() method will always fail when comparing a non-proxy B instance to a proxy B instance, because it compares the classes of both objects:

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

    In the case of Hibernate entities, you should replace this with

    if (!(obj instanceof B)) {
    return false;
}

    Also, note that