在many-to-one, one-to-one, 关系中，一方引入另一方的属性，如果引用属性值数据在数据库中不见，hibernate默认会抛出异常，解决此问题，加@NotFound注解即可.@notFound注解默认值为NotFoundAction.EXCEPTION
@ManyToOne
@JoinColumn(name="area_id")
@NotFound(action = NotFoundAction.IGNORE)
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public Area getArea() {
return area;
}
