Hibernate4学习总结(4)--注解形式的集合映射，关联关系映射

      本文将接着上文，讲解hibernate4的集合映射的注解和关联关系映射的注解。本文包括两个部分：

1. 集合映射的注解。
2. 关联关系映射的注解。

一、集合映射的注解

         当持久化中有一个属性是集合(Set、List、Map)，就要用到集合映射。集合属性会单独生成一张表。定义集合属性时面向接口，并且集合属性需要程序员自己初始化（例如：private List list = new ArrayList();）。

集合属性都要用到的注解：

• @ElementCollection(fetch="该属性的加载策略"，targetClass="集合中元素的类型")。
         fetch=FetchType.EAGER: 立即加载
         fetch=FetchType.LAZY: 延迟加载
• @CollectionTable(name="表名") : 指定集合生成表的相关信息。

1.1 List集合映射(有序集合): @OrderColumn() 指定排序列

注意：List集合生成表的主键列：（外键列 + 排序列）

1.1.1 List : 集合中元素是标量类型 8个基本类型、包装类、String。

例如：Employee类

package edu.scut.e_CollectionMapping_List;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.*;

@Entity
@Table(name="EMP_INFO")
public class Employee implements Serializable {
	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
 	private String name;
 	private int age;
	
 	@ElementCollection(fetch=FetchType.LAZY, //加载策略,延迟加载
			targetClass=String.class) //指定集合中元素的类型
 	@CollectionTable(name="ADD_INFO") //指定集合生成的表
	@OrderColumn(name="O_ID") //指定排序列的名称
 	private List address = new ArrayList();
 	public int getId() {
		return id;
 	}
 	public List getAddress() {
 		return address;
	}
	public void setAddress(List address) {
		this.address = address;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
}

生成两张表：

emp_info表

add_info表

1.1.2 List

: 集合中元素是复合类型。复合属性类上需要加注解：@Embeddable。

例如：Person类

package edu.scut.e_CollectionMapping_List;

import java.util.ArrayList;
import java.util.List;
import javax.persistence.*;

@Entity
@Table(name="PER_INFO")
public class Person {
	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
  	private String name;
	
	@ElementCollection(fetch=FetchType.LAZY, //加载策略
  			targetClass=Address.class) //指定元素中集合的类型
	@CollectionTable(name="PER_ADD_INFO") //指定集合生成的表
	 @OrderColumn(name="O_A_ID") //指定排序列的名称
 	private List
 address = new ArrayList
();
  	public int getId() {
  		return id;
 	}
 	public void setId(int id) {
 		this.id = id;
  	}
 	public String getName() {
  		return name;
  	}
 	public void setName(String name) {
 		this.name = name;
  	}
	public List
 getAddress() {
   		return address;
  	}
 	public void setAddress(List
 address) {
   		this.address = address;
 	}
}

Address类

package edu.scut.e_CollectionMapping_List;

import javax.persistence.Embeddable;

@Embeddable
public class Address {
	private String zip;
	private String info;
	public String getZip() {
		return zip;
	}
	public void setZip(String zip) {
		this.zip = zip;
	}
	public String getInfo() {
		return info;
	}
	public void setInfo(String info) {
		this.info = info;
	}
}

生成的两张表：

per_info表

per_add_info表

1.2 Set集合映射(无序集合)

注意： Set集合生成表的主键列：（外键列 + Set集合的元素列 .. ）

1.2.1· Set : 集合中元素是标量类型 8个基本类型、包装类、String。

           Set集合生成表默认是没有主键列的。如果想要生成主键列，需要为Set集合添加非空约束！

例如：Employee类

package edu.scut.e_CollectionMapping_Set;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import javax.persistence.*;

@Entity
@Table(name="EMP_INFO")
public class Employee implements Serializable {
 	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
 	private String name;
 	private int age;
	
	@ElementCollection(fetch=FetchType.LAZY, //加载策略,延迟加载
 			targetClass=String.class) //指定集合中元素的类型
	@CollectionTable(name="ADD_INFO") //指定集合生成的表
	@Column(nullable=false) //添加非空约束
 	private Set address = new HashSet();
	public int getId() {
 		return id;
	}
 	public Set getAddress() {
 		return address;
 	}
	public void setAddress(Set address) {
  		this.address = address;
  	}

 	public void setId(int id) {
 		this.id = id;
  	}
 	public String getName() {
 		return name;
 	}
   	public void setName(String name) {
  		this.name = name;
  	}
 	public int getAge() {
  		return age;
  	}
   	public void setAge(int age) {
  		this.age = age;
   	}
}

1.2.2  Set

: 集合中元素是复合类型。
          复合属性类上需要加注解：@Embeddable
         Set集合生成表默认是没有主键列的。如果想要生成主键列，需要为Set集合的元素类的属性上添加非空约束！

例如：Person类

package edu.scut.e_CollectionMapping_Set;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import javax.persistence.*;

@Entity
@Table(name="PER_INFO")
public class Person {
	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
  	private String name;
	
  	@ElementCollection(fetch=FetchType.LAZY, //加载策略
  			targetClass=Address.class) //指定元素中集合的类型
  	@CollectionTable(name="PER_ADD_INFO") //指定集合生成的表

  	private Set
 address = new HashSet
();
 	public int getId() {
  		return id;
	}
   	public void setId(int id) {
  		this.id = id;
  	}
  	public String getName() {
 		return name;
   	}
 	public void setName(String name) {
 		this.name = name;
  	}
 	public Set
 getAddress() {
 		return address;
 	}
	public void setAddress(Set
 address) {
  		this.address = address;
 	}
}

Address类

package edu.scut.e_CollectionMapping_Set;

import javax.persistence.Column;
import javax.persistence.Embeddable;

@Embeddable
public class Address {
	//@Column(nullable=false)
	private String zip;
	@Column(nullable=false)
	private String info;
	public String getZip() {
		return zip;
	}
	public void setZip(String zip) {
		this.zip = zip;
	}
	public String getInfo() {
		return info;
	}
	public void setInfo(String info) {
		this.info = info;
	}
}

1.3 Map集合映射(有Map的key)： @MapKeyColumn() 指定Map的key生成的列

注意： Map集合生成表的主键列：（外键列 + Map的Key）

1.3.1 Map : 集合中元素是标量类型 8个基本类型、包装类、String。

例如：Employee类

package edu.scut.e_CollectionMapping_Map;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.persistence.*;

@Entity
@Table(name="EMP_INFO")
public class Employee implements Serializable {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
 	private String name;
	private int age;
	
 	@ElementCollection(fetch=FetchType.LAZY, //加载策略,延迟加载
			targetClass=String.class) //指定集合中元素的类型
 	@CollectionTable(name="ADD_INFO") //指定集合生成的表
	@MapKeyColumn(name="M_KEY") //指定map的key生成的列
 	private Map address = new HashMap();
 	public int getId() {
 		return id;
	}
	public Map getAddress() {
 		return address;
 	}
	public void setAddress(Map address) {
 		this.address = address;
 	}
  	public void setId(int id) {
		this.id = id;
	}
  	public String getName() {
 		return name;
 	}
 	public void setName(String name) {
		this.name = name;
  	}
  	public int getAge() {
 		return age;
 	}
  	public void setAge(int age) {
  		this.age = age;
	}
}

1.3.2 Map : 集合中元素是复合类型。
         复合属性类上需要加注解：@Embeddable

例如：Person类

package edu.scut.e_CollectionMapping_Map;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javax.persistence.*;

@Entity
@Table(name="PER_INFO")
public class Person {
 	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
 	private int id;
 	private String name;
 	
  	@ElementCollection(fetch=FetchType.LAZY, //加载策略
 			targetClass=Address.class) //指定元素中集合的类型
  	@CollectionTable(name="PER_ADD_INFO") //指定集合生成的表
 	@MapKeyColumn(name="ADD_KEY") //指定key生成的列
	private Map address = new HashMap();
  	public int getId() {
 		return id;
  	}
	public void setId(int id) {
 		this.id = id;
 	}
 	public String getName() {
 		return name;
  	}
 	public void setName(String name) {
  		this.name = name;
	}
 	public Map getAddress() {
  		return address;
 	}
 	public void Address(Map address) {
  		this.address = address;
  	}
}

Address类

package edu.scut.e_CollectionMapping_Map;

import javax.persistence.Column;
import javax.persistence.Embeddable;

@Embeddable
public class Address {
	//@Column(nullable=false)
	private String zip;
	@Column(nullable=false)
	private String info;
	public String getZip() {
		return zip;
	}
	public void setZip(String zip) {
		this.zip = zip;
	}
	public String getInfo() {
		return info;
	}
	public void setInfo(String info) {
		this.info = info;
	}
}

二、关联关系映射的注解（重点）

单向关联映射和双向关联映射的最大区别就是在查询数据时，单向关联只能通过一边进行查询，而双向关联两边都可以互相查询。

2.1 单向关联映射（一边配置）

2.1.1 一对一

/** 一方*/
@OneToOne(fetch=FetchType.LAZY,
		cascade=CascadeType.ALL,
		targetEntity=Persons.class)  //维护关联关系（从表）
/** 生成外键列*/
@JoinColumn(name="P_ID",unique=true,referencedColumnName="id")

通过公民（Person）和身份证(IdCards)的例子来说明：

Person.java

package edu.scut.f_AssoMap_single_one2one;

import javax.persistence.*;

//公民（一方）
@Entity
@Table(name="PER_INFO")
public class Persons {
 	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
 	private int id;
  	private String name;
	
 	public int getId() {
 		return id;
  	}
 	public void setId(int id) {
 		this.id = id;
   	}
 	public String getName() {
		return name;
   	}
	public void setName(String name) {
  		this.name = name;
 	}
}

IdCards.java

package edu.scut.f_AssoMap_single_one2one;

import javax.persistence.*;

//身份证（一方）
@Entity
@Table(name="IDCD_INFO")
public class IdCards {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="IDCD_ID")
	private int id;
	private String cardno;
	
	/** 一方*/
	@OneToOne(fetch=FetchType.LAZY,
			cascade=CascadeType.ALL,
			targetEntity=Persons.class)  //维护关联关系（从表）
	/** 生成外键列*/
	@JoinColumn(name="P_ID",unique=true,referencedColumnName="id")
	private Persons persons;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getCardno() {
		return cardno;
	}
	public void setCardno(String cardno) {
		this.cardno = cardno;
	}
	public Persons getPersons() {
		return persons;
	}
	public void setPersons(Persons persons) {
		this.persons = persons;
	}
}

2.1.2 一对多

/** 一方*/
 @OneToMany(fetch=FetchType.LAZY, //延迟加载
		targetEntity=Orders.class, //目标对象
 		cascade=CascadeType.ALL,//级联操作
 		orphanRemoval=true)  //孤儿删除
 @JoinColumn(name="C_ID",referencedColumnName="CUS_ID")

通过客户（Customers）和订单(Orders)的例子说明：

Customers.java

package edu.scut.f_AssoMap_single_one2n;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.*;

//客户（一方）
@Entity
@Table(name="CUS_INFO")
public class Customers {
	@Id
        @GeneratedValue(strategy=GenerationType.AUTO)
 	@Column(name="CUS_ID")
	private int id;
 	private String name;
	
	/** 一方*/
 	@OneToMany(fetch=FetchType.LAZY, //延迟加载
			targetEntity=Orders.class, //目标对象
 			cascade=CascadeType.ALL,//级联操作
 			orphanRemoval=true)  //孤儿删除
 	@JoinColumn(name="C_ID",referencedColumnName="CUS_ID")
	private Set orders = new HashSet();
 	public int getId() {
		return id;
 	}
 	public void setId(int id) {
 		this.id = id;
 	}
  	public String getName() {
 		return name;
   	}
 	public void setName(String name) {
 		this.name = name;
  	}
   	public Set getOrders() {
 		return orders;
   	}
  	public void setOrders(Set orders) {
 		this.orders = orders;
    	}
}

Orders.java

package edu.scut.f_AssoMap_single_one2n;

import javax.persistence.*;;
import javax.persistence.Table;

//订单（多方）
@Entity
@Table(name="ORD_INFO")
public class Orders {
 	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
  	private int id;
 	private String orderno;
	
  	public int getId() {
 		return id;
  	}
  	public void setId(int id) {
 		this.id = id;
  	}
   	public String getOrderno() {
		return orderno;
   	}
 	public void setOrderno(String orderno) {
  		this.orderno = orderno;
 	}
}

2.1.3 多对一

/** 多方*/
 @ManyToOne(fetch=FetchType.LAZY,
 		cascade=CascadeType.ALL,
 		targetEntity=Customers.class)
/** 生成外键列*/
@JoinColumn(name="C_ID",referencedColumnName="CUS_ID")

通过客户（Customers）和订单(Orders)的例子说明：

Customers.java

package edu.scut.f_AssoMap_single_n2one;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.*;

//客户（一方）
@Entity
@Table(name="CUS_INFO")
public class Customers {
	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
 	@Column(name="CUS_ID")
	private int id;
  	private String name;

   	public int getId() {
  		return id;
  	}
  	public void setId(int id) {
   		this.id = id;
  	}
 	public String getName() {
    		return name;
	}
   	public void setName(String name) {
 		this.name = name;
   	}
}

Orders.java

package edu.scut.f_AssoMap_single_n2one;

import javax.persistence.*;

//订单（多方）
@Entity
@Table(name="ORD_INFO")
public class Orders {
	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
  	private int id;
  	private String orderno;
	
  	/** 多方*/
 	@ManyToOne(fetch=FetchType.LAZY,
  			cascade=CascadeType.ALL,
  			targetEntity=Customers.class)
 	/** 生成外键列*/
   	@JoinColumn(name="C_ID",referencedColumnName="CUS_ID")
  	private Customers customers;
	
 	public int getId() {
  		return id;
 	}
  	public void setId(int id) {
   		this.id = id;
 	}
   	public String getOrderno() {
  		return orderno;
  	}
  	public void setOrderno(String orderno) {
		this.orderno = orderno;
  	}
	public Customers getCustomers() {
 		return customers;
  	}
 	public void setCustomers(Customers customers) {
		this.customers = customers;
  	}
	
}

2.1.4 多对多

/** 多方*/
@ManyToMany(fetch=FetchType.LAZY, //延迟加载
		cascade=CascadeType.ALL,
		targetEntity=Teacher.class) //目标对象
/** 中间表*/
@JoinTable(name="TEA_STU", //指定中间表名称
		joinColumns=@JoinColumn(name="S_ID",referencedColumnName="STU_ID"), //@ManyToMany中没有加mappedby的主键列
		inverseJoinColumns=@JoinColumn(name="T_ID",referencedColumnName="TEA_ID")) //@ManyToMany中加mappedby的主键列	

通过老师（Teachers）和学生(Students)的例子说明：

Teachers.java

package edu.scut.f_AssoMap_single_n2n;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.*;

//多方
@Entity
@Table(name="TEA_INFO")
public class Teacher {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="TEA_ID")
 	private int id;
 	private String name;
	private String dept;
 	public int getId() {
		return id;
 	}
 	public void setId(int id) {
		this.id = id;
  	}
 	public String getName() {
 		return name;
 	}
 	public void setName(String name) {
 		this.name = name;
	}
  	public String getDept() {
 		return dept;
 	}
 	public void setDept(String dept) {
 		this.dept = dept;
 	}
}

Students.java

package edu.scut.f_AssoMap_single_n2n;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.*;

//多方
@Entity
@Table(name="STU_INFO")
public class Student {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="STU_ID")
	private int id;
	private String name;
	private float score;
	
	/** 多方*/
	@ManyToMany(fetch=FetchType.LAZY, //延迟加载
			cascade=CascadeType.ALL,
			targetEntity=Teacher.class) //目标对象
	/** 中间表*/
	@JoinTable(name="TEA_STU", //指定中间表名称
			joinColumns=@JoinColumn(name="S_ID",referencedColumnName="STU_ID"), //@ManyToMany中没有加mappedby的主键列
			inverseJoinColumns=@JoinColumn(name="T_ID",referencedColumnName="TEA_ID")) //@ManyToMany中加mappedby的主键列	
	private Set teachers = new HashSet();
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public float getScore() {
		return score;
	}
	public void setScore(float score) {
		this.score = score;
	}
	public Set getTeachers() {
		return teachers;
	}
	public void setTeachers(Set teachers) {
		this.teachers = teachers;
	}
}

2.2 双向关联映射（两边同时配置）

2.2.1 一对一

一方：

/** 一方 */
@OneToOne(fetch=FetchType.LAZY,
	targetEntity=IdCards.class,
	mappedBy="persons",   //不维护关联关系（主表）
	cascade=CascadeType.ALL) 

另一方：

/** 一方*/
@OneToOne(fetch=FetchType.LAZY,
		targetEntity=Persons.class)  //维护关联关系（从表）
/** 生成外键列*/
@JoinColumn(name="P_ID",unique=true,referencedColumnName="id")

还是通过公民（Persons）和身份证(IdCards)的例子来说明：

Persons.java

package edu.scut.f_AssoMap_double_one2one;

import javax.persistence.*;

//公民（一方）
@Entity
@Table(name="PER_INFO")
public class Persons {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	private String name;
	
	/** 一方 */
	@OneToOne(fetch=FetchType.LAZY,
			targetEntity=IdCards.class,
			mappedBy="persons",   //不维护关联关系（主表）
			cascade=CascadeType.ALL) 
	private IdCards idcards;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public IdCards getIdcards() {
		return idcards;
	}
	public void setIdcards(IdCards idcards) {
		this.idcards = idcards;
	}
}

IdCards.java

package edu.scut.f_AssoMap_double_one2one;

import javax.persistence.*;

//身份证（一方）
@Entity
@Table(name="IDCD_INFO")
public class IdCards {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="IDCD_ID")
	private int id;
	private String cardno;
	
	/** 一方*/
	@OneToOne(fetch=FetchType.LAZY,
			targetEntity=Persons.class)  //维护关联关系（从表）
	/** 生成外键列*/
	@JoinColumn(name="P_ID",unique=true,referencedColumnName="id")
	private Persons persons;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getCardno() {
		return cardno;
	}
	public void setCardno(String cardno) {
		this.cardno = cardno;
	}
	public Persons getPersons() {
		return persons;
	}
	public void setPersons(Persons persons) {
		this.persons = persons;
	}
}

2.2.2 一对多

一方：

/** 一方*/
@OneToMany(fetch=FetchType.LAZY, //延迟加载
		targetEntity=Orders.class, //目标对象
		cascade=CascadeType.ALL,  //级联操作
		orphanRemoval=true,  //孤儿删除
		mappedBy="customers") //指定由哪边维护关系(从表维护)

多方：

/** 多方*/
	@ManyToOne(fetch=FetchType.LAZY,
			//cascade=CascadeType.ALL,
			targetEntity=Customers.class)
	/** 生成外键列*/
	@JoinColumn(name="C_ID",referencedColumnName="CUS_ID")

还是通过客户（Customers）和订单(Orders)的例子说明：

Customers.java

package edu.scut.f_AssoMap_double_one2n;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.*;

//客户（一方）
@Entity
@Table(name="CUS_INFO")
public class Customers {
	@Id
 	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="CUS_ID")
	private int id;
 	private String name;
	
 	/** 一方*/
	@OneToMany(fetch=FetchType.LAZY, //延迟加载
 			targetEntity=Orders.class, //目标对象
			cascade=CascadeType.ALL,  //级联操作
 			orphanRemoval=true,  //孤儿删除
			mappedBy="customers") //指定由哪边维护关系(从表维护)
	private Set orders = new HashSet();
	public int getId() {
  		return id;
	}
	public void setId(int id) {
 		this.id = id;
 	}
 	public String getName() {
		return name;
 	}
 	public void setName(String name) {
 		this.name = name;
 	}
	public Set getOrders() {
 		return orders;
 	}
	public void setOrders(Set orders) {
  		this.orders = orders;
 	}
}

Orders.java

package edu.scut.f_AssoMap_double_one2n;

import javax.persistence.*;

//订单（多方）
@Entity
@Table(name="ORD_INFO")
public class Orders {
 	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
 	private int id;
 	private String orderno;
	
 	/** 多方*/
 	@ManyToOne(fetch=FetchType.LAZY,
			//cascade=CascadeType.ALL,
 			targetEntity=Customers.class)
	/** 生成外键列*/
 	@JoinColumn(name="C_ID",referencedColumnName="CUS_ID")
 	private Customers customers;
	
	public int getId() {
 		return id;
 	}
 	public void setId(int id) {
		this.id = id;
  	}
 	public String getOrderno() {
		return orderno;
  	}
	public void setOrderno(String orderno) {
 		this.orderno = orderno;
 	}
 	public Customers getCustomers() {
 		return customers;
 	}
 	public void setCustomers(Customers customers) {
		this.customers = customers;
 	}
	
}

2.2.3 多对多

多方：

/** 多方*/
	@ManyToMany(fetch=FetchType.LAZY, //延迟加载
			targetEntity=Student.class, //指定目标对象
			cascade=CascadeType.ALL,
			mappedBy="teachers") //老师不维护关联关系

另一个多方：

/** 多方*/
	@ManyToMany(fetch=FetchType.LAZY, //延迟加载
			targetEntity=Teacher.class) //目标对象
	/** 中间表*/
	@JoinTable(name="TEA_STU", //指定中间表名称
			joinColumns=@JoinColumn(name="S_ID",referencedColumnName="STU_ID"), //@ManyToMany中没有加mappedby的主键列
			inverseJoinColumns=@JoinColumn(name="T_ID",referencedColumnName="TEA_ID")) //@ManyToMany中加mappedby的主键列	

还是通过老师（Teachers）和学生(Students)的例子说明：

Teachers.java

package edu.scut.f_AssoMap_double_n2n;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.*;

//多方
@Entity
@Table(name="TEA_INFO")
public class Teacher {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="TEA_ID")
	private int id;
	private String name;
	private String dept;
	
	/** 多方*/
	@ManyToMany(fetch=FetchType.LAZY, //延迟加载
			targetEntity=Student.class, //目标对象
			cascade=CascadeType.ALL,
			mappedBy="teachers") //老师不维护关联关系
	private Set students = new HashSet();
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
 	}
	public String getName() {
 		return name;
 	}
	public void setName(String name) {
 		this.name = name;
	}
 	public String getDept() {
		return dept;
	}
  	public void setDept(String dept) {
		this.dept = dept;
 	}
	public Set getStudents() {
 		return students;
	}
 	public void setStudents(Set students) {
		this.students = students;
 	}
}

Students.java

package edu.scut.f_AssoMap_double_n2n;

import java.util.HashSet;
import java.util.Set;
import javax.persistence.*;

//多方
@Entity
@Table(name="STU_INFO")
public class Student {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="STU_ID")
	private int id;
	private String name;
	private float score;
	
	/** 多方*/
	@ManyToMany(fetch=FetchType.LAZY, //延迟加载
			targetEntity=Teacher.class) //目标对象
 	/** 中间表*/
	@JoinTable(name="TEA_STU", //指定中间表名称
 			joinColumns=@JoinColumn(name="S_ID",referencedColumnName="STU_ID"), //@ManyToMany中没有加mappedby的主键列
			inverseJoinColumns=@JoinColumn(name="T_ID",referencedColumnName="TEA_ID")) //@ManyToMany中加mappedby的主键列	
	private Set teachers = new HashSet();
 	public int getId() {
		return id;
	}
 	public void setId(int id) {
		this.id = id;
 	}
	public String getName() {
 		return name;
	}
 	public void setName(String name) {
		this.name = name;
 	}
	public float getScore() {
 		return score;
	}
 	public void setScore(float score) {
		this.score = score;
	}
 	public Set getTeachers() {
		return teachers;
 	}
	public void setTeachers(Set teachers) {
 		this.teachers = teachers;
 	}
}