Hibernate进级篇
定义两个实体对象： Order 实体 @Entity @Table(name="orders") public class Order { //1-m,多的一方为关系维护端，关系维护端负责外键记录的更新，关系被维护端没有权利更新外键记录 private String orderid; private Float amount; private Set<OrderItem> items = new HashSet<OrderItem>(); @Id @Column(length=12) public String getOrderid() { return orderid; } public void setOrderid(String orderid) { this.orderid = orderid; } @Column(nullable=false) public Float getAmount() { return amount; } public void setAmount(Float amount) { this.amount = amount; } @OneToMany(cascade={CascadeType.REFRESH,CascadeType.PERSIST,CascadeType.REMOVE,CascadeType.MERGE},fetch