.NET Information center: Hibernate, lazy loading and inheritance

Wednesday, March 10, 2010

Hibernate, lazy loading and inheritance

A common problem with typecasting a lazy loaded entity to its child is a ClassCastException. This exception occurs because the dynamic created proxy implements the baseclass and has no knowledge about its subclasses.

Suppose we have a class B which extends A and a class C which has class A as a member as shown below.

public class A
{
private Long id;
private String name;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public Long getId() { return id; }
}

public class B extends A
{
private String somethingElse;
public String getSomethingElse() { return somethingElse; }
public void setSomethingElse(String something) { this.somethingElse = something; }
}

public class C
{
private Long id;
private A a;
public A getA() { return a; }
public void setA(A a) { this.a = a; }
public Long getId() { return id; }
}