hibernate annotation多对多问题：insert关系前先delete

yiqingfeng0215

我用hbiernate annation写的代码，维护多对多关系时，出了个奇怪的问题：

1：Operator.java

@Entity //@Table(name="operator" public class Operator implements java.io.Serializable,IfTableModel {     private static final long serialVersionUID = 1L;     public static final String [] column={"编号","姓名","其他信息"};         @Id     @GeneratedValue(strategy = GenerationType.AUTO)     @Column(name = "id")     private Integer id;     @Column(name = "name",unique=true)     private String name;     @Column(name = "msg")     private String msg;         @ManyToOne(targetEntity=base.Role.class)//,cascade={CascadeType.PERSIST,CascadeType.MERGE} )     @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})     @JoinColumn(name="RoleId")     private Role role;         @ManyToMany(targetEntity=base.Department.class)     @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})     @JoinTable(         name="operator_department ",         joinColumns={@JoinColumn(name="OperatorId")},         inverseJoinColumns={@JoinColumn(name="DepartId")}             )     private List<Department> departs=new ArrayList(); }

2epartment.java

@Entity @Table(name = "department") public class Department implements java.io.Serializable,IfTableModel {     private static final long serialVersionUID = 1L;     public static final String Id = "id";     public static final String Name = "name";     public static final String [] column={"编号","部门名称"};         @Id     @GeneratedValue(strategy = GenerationType.AUTO)     @Column(name = "id")     private Integer id;     @Column(name = "name")     private String name;     @ManyToMany(targetEntity=base.Operator.class,mappedBy="departs")     private List<Operator> operators=new ArrayList();     }

关系说明：operator和department是多对多的关系，其中，operator端负责关系的维护
3:对operator和department操作的代码

Transaction tx2= se.beginTransaction();         BaseUtil u=new BaseUtil();         List<Department> departs=u.getDepartments();         List<Operator> opers=u.getOperators();         opers.get(0).getDeparts().add(departs.get(0));         opers.get(0).getDeparts().add(departs.get(1));         tx2.commit();

现在期望的sql代码是：insert into operator_department  (OperatorId, DepartId) values (?, ?)
这里出现一个奇怪的问题是，现在总是先
delete from operator_department  where OperatorId=?
然后才把所有原来的关系重新插入一遍
insert into operator_department  (OperatorId, DepartId) values (?, ?)
insert into operator_department  (OperatorId, DepartId) values (?, ?)
insert into operator_department  (OperatorId, DepartId) values (?, ?)
这样严重影响性能，各位高人帮忙看看什么原因啊？

yiqingfeng0215

没有人知道么？