2.2、Hibernate用註解方式實現一對多、多對多關系
阿新 • • 發佈：2017-12-29
tab 技術部 employee join incr 無法運行 hset strategy urn 
一、一對多關系
1、在上一篇日誌中用.xml配置文件項目基礎上，再往lib目錄先添加一個包-hibernate-jpa-2.0-api-1.0.0.Final.jar
2、新建一個com.st.bean4 包，往包裏面添加兩個含有註解的類：
a)、DeptBean2類：
1 package com.st.bean4; 2 3 import java.util.HashSet; 4 import java.util.Set; 5 6 7 import javax.persistence.Column; 8 import javax.persistence.Entity; 9 import javax.persistence.GeneratedValue; 10 import javax.persistence.Id; 11 import javax.persistence.JoinColumn; 12 import javax.persistence.OneToMany; 13 import javax.persistence.Table; 14 15 import org.hibernate.annotations.Cascade; 16 import org.hibernate.annotations.CascadeType; 17 import org.hibernate.annotations.GenericGenerator; 18 19 @Entity //指定實體類 20 @Table(name="DEPT") //對應表的名稱 21 @GenericGenerator(name="genID", strategy="increment") //聲明主鍵生成策略 22 public class DeptBean2 { 23 @Id //指定主鍵 24 @GeneratedValue(generator="genID") //設定主鍵生成策略 25 @Column(name="ID") //指定類中的屬性與表中的列的對應關系 26 private long id; 27 @Column(name="NAME") //指定類中的屬性與表中的列的對應關系 28 private String name; 29 30 @OneToMany //指定一對多關系 31 @Cascade(value={CascadeType.SAVE_UPDATE}) //設定級聯關系 32 @JoinColumn(name="dept_id") //指定與本類主鍵所對應的外表的外鍵 33 private Set<EmployeeBean2> emp = new HashSet<EmployeeBean2>(); 34 @Override 35 public String toString() { 36 return "DeptBean [id=" + id + ", name=" + name +"]"; 37 } 38 public long getId() { 39 return id; 40 } 41 public void setId(long id) { 42 this.id = id; 43 } 44 public String getName() { 45 return name; 46 } 47 public void setName(String name) { 48 this.name = name; 49 } 50 public Set<EmployeeBean2> getEmp() { 51 return emp; 52 } 53 public void setEmp(Set<EmployeeBean2> emp) { 54 this.emp = emp; 55 } 56 }
b）、EmployeeBean類：
1 package com.st.bean4; 2 3 import javax.persistence.Column; 4 import javax.persistence.Entity; 5 import javax.persistence.GeneratedValue; 6 import javax.persistence.Id; 7 import javax.persistence.JoinColumn; 8 import javax.persistence.ManyToOne; 9 import javax.persistence.Table; 10 11 import org.hibernate.annotations.GenericGenerator; 12 13 @Entity //指定一個實體 14 @Table(name="employee") //指定表的名稱 15 @GenericGenerator(name="genID", strategy="increment") //聲明主鍵生成策略 16 public class EmployeeBean2 { 17 @Id //指定主鍵 18 @GeneratedValue(generator="genID") //設定主鍵生成策略 19 @Column(name="ID") //類中的屬性和表中的列名的對應關系 20 private long id; 21 @Column(name="NAME") 22 private String name; 23 @Column(name="SEX") 24 private String sex; 25 @Column(name="JOB") 26 private String job; 27 @ManyToOne// 指定多對一關系 //指定多對一關系 28 @JoinColumn(name="DEPT_ID") 29 //一個員工對應於一個部門號，所以這裏不用集合 30 private DeptBean2 dept ; //註意這個地方不要new對象，否則會無法運行 31 public long getId() { 32 return id; 33 } 34 public void setId(long id) { 35 this.id = id; 36 } 37 public String getName() { 38 return name; 39 } 40 public void setName(String name) { 41 this.name = name; 42 } 43 public String getSex() { 44 return sex; 45 } 46 public void setSex(String sex) { 47 this.sex = sex; 48 } 49 public String getJob() { 50 return job; 51 } 52 public void setJob(String job) { 53 this.job = job; 54 } 55 public DeptBean2 getDept() { 56 return dept; 57 } 58 public void setDept(DeptBean2 dept) { 59 this.dept = dept; 60 } 61 @Override 62 public String toString() { 63 return "EmployeeBean [id=" + id + ", name=" + name + ", sex=" + sex 64 + ", job=" + job + ", dept=" + dept 65 + "]"; 66 } 67 }
3、在hibernate.cfg.xml文件中引入上面兩個類的映射
1 <mapping class="com.st.bean5.UserBean2" />
2 <mapping class="com.st.bean5.RoleBean2" />
4、在BeanTest中添加相應的測試方法：
1 @Test 2 public void bean4test1(){ 3 Session session = HibernateTools.openSession(); 4 Transaction tran = session.beginTransaction(); 5 //首先在dept中新增一條數據，再關聯的在employee中新增一條數據 6 //DeptBean2 dept = new DeptBean2(); 7 //先讀去dept中的數據，再在讀取的基礎上關聯的在employee中新增一條數據 8 DeptBean2 dept = (DeptBean2) session.get(DeptBean2.class,1L); //1L代表主鍵 9 EmployeeBean2 emp = new EmployeeBean2(); 10 //dept.setName("技術部"); 11 emp.setName("陳澤俊"); 12 emp.setSex("男"); 13 emp.setJob("STM32"); 14 dept.getEmp().add(emp); 15 session.save(dept); 16 //確認提交事物 17 tran.commit(); 18 }
二、多對多關系
1、新建一個com.st.bean4 包，往包裏面添加兩個含有註解的類
a）、UserBean2：
1 package com.st.bean5;
2 import java.util.HashSet;
3 import java.util.Set;
4
5 import javax.persistence.Column;
6 import javax.persistence.Entity;
7 import javax.persistence.GeneratedValue;
8 import javax.persistence.Id;
9 import javax.persistence.JoinColumn;
10 import javax.persistence.JoinTable;
11 import javax.persistence.ManyToMany;
12 import javax.persistence.Table;
13
14 import org.hibernate.annotations.Cascade;
15 import org.hibernate.annotations.CascadeType;
16 import org.hibernate.annotations.GenericGenerator;
17
18 @Entity //實體
19 @Table(name="T_USER") //表名
20 @GenericGenerator(name="genID", strategy="increment") //聲明主鍵生成策略
21 public class UserBean2 {
22 @Id //指定主鍵
23 @GeneratedValue(generator="genID") //設定主鍵生成策略
24 @Column(name="ID") //指定類的屬性和表的字段的對應關系
25 private long id;
26 @Column(name="NAME")
27 private String name;
28 @Column(name="SEX")
29 private String sex;
30 @ManyToMany //指定多對多關系
31 @Cascade(value={CascadeType.SAVE_UPDATE}) //設置級聯關系
32 @JoinTable(name="USER_ROLE", //指定第三張表
33 joinColumns={@JoinColumn(name="USER_ID")}, //本表與中間表的外鍵對應
34 inverseJoinColumns={@JoinColumn(name="ROLE_ID")}) //另一張表與第三張表的外鍵的對應關系
35 private Set<RoleBean2> role = new HashSet<RoleBean2>();
36 public long getId() {
37 return id;
38 }
39 public void setId(long id) {
40 this.id = id;
41 }
42 public String getName() {
43 return name;
44 }
45 public void setName(String name) {
46 this.name = name;
47 }
48 public String getSex() {
49 return sex;
50 }
51 public void setSex(String sex) {
52 this.sex = sex;
53 }
54 public Set<RoleBean2> getRole() {
55 return role;
56 }
57 public void setRole(Set<RoleBean2> role) {
58 this.role = role;
59 }
60 @Override
61 public String toString() {
62 return "UserBean [id=" + id + ", name=" + name + ", sex=" + sex
63 + ", role=" + role + "]";
64 }
65 }
b）、RoleBean類：
1 package com.st.bean5;
2 import java.util.HashSet;
3
4 import java.util.Set;
5
6 import javax.persistence.Column;
7 import javax.persistence.Entity;
8 import javax.persistence.GeneratedValue;
9 import javax.persistence.Id;
10 import javax.persistence.JoinColumn;
11 import javax.persistence.JoinTable;
12 import javax.persistence.ManyToMany;
13 import javax.persistence.Table;
14
15 import org.hibernate.annotations.Cascade;
16 import org.hibernate.annotations.CascadeType;
17 import org.hibernate.annotations.GenericGenerator;
18
19 @Entity //實體
20 @Table(name="T_ROLE") //表名
21 @GenericGenerator(name="genID", strategy="increment")//聲明主鍵生成策略
22 public class RoleBean2 {
23 @Id //主鍵
24 @GeneratedValue(generator="genID") //設置主鍵生成策略
25 @Column(name="ID") //類中的屬性與表的字段的對應關系
26 private long id;
27 @Column(name="POST")
28 private String post;//職位
29 @Column(name="PAY")
30 private int pay; //薪資
31 @ManyToMany //多對多關系
32 @Cascade(value={CascadeType.SAVE_UPDATE}) //級聯關系
33 @JoinTable(name="USER_ROLE", //中間表的名稱
34 joinColumns={@JoinColumn(name="ROLE_ID")}, //本表與中間表的外鍵對應關系
35 inverseJoinColumns={@JoinColumn(name="USER_ID")}) //另一張表與中間表的外鍵的對應關系
36 private Set<UserBean2> user = new HashSet<UserBean2>();
37
38 public long getId() {
39 return id;
40 }
41 public void setId(long id) {
42 this.id = id;
43 }
44 public String getPost() {
45 return post;
46 }
47 public void setPost(String post) {
48 this.post = post;
49 }
50 public int getPay() {
51 return pay;
52 }
53 public void setPay(int pay) {
54 this.pay = pay;
55 }
56 public Set<UserBean2> getUser() {
57 return user;
58 }
59 public void setUser(Set<UserBean2> user) {
60 this.user = user;
61 }
62 @Override
63 public String toString() {
64 return "RoleBean [id=" + id + ", post=" + post + ", pay=" + pay + "]";
65 }
66 }
2、在hibernate.cfg.xml中引入UserBean2和RoleBean2這兩個類的映射：
1 <mapping class="com.st.bean5.UserBean2" />
2 <mapping class="com.st.bean5.RoleBean2" />
3、在BeanTest類中添加測試方法：
1 @Test
2 public void bean5test1(){
3 // 獲取一個會話
4 Session session = HibernateTools.openSession();
5 //開啟一次事物
6 Transaction tran = session.beginTransaction();
7 UserBean2 user = new UserBean2();
8 // RoleBean2 role = (RoleBean2) session.get(RoleBean2.class,1L);
9 RoleBean2 role = new RoleBean2();
10
11 user.setName("汪文仕");
12 user.setSex("男");
13
14 role.setPost("博士");
15 role.setPay(10000);
16
17 role.getUser().add(user);
18 session.save(role);
19 //確認提交事物
20 tran.commit();
21 }
22 @Test
23 public void bean5test2(){
24 // 獲取一個會話
25 Session session = HibernateTools.openSession();
26 /* List<UserBean> list = session.createCriteria(UserBean.class).list();
27 for(UserBean user : list)
28 System.out.println(user);*/
29 String hql = "select new Map(u.name as name,u.sex as sex,r.post as post,r.pay as pay) from UserBean2 u join u.role r";
30 List<Map<String,Object>> list = session.createQuery(hql).list();
31 for(Map<String,Object> data : list)
32 System.out.println(data);
33 }
三、註意：
1、引入了註解需要的jar包後要先刪除Java EE 5 Library這個庫，否則會兩個jar包中的類產生沖突
2、在多表操作時最好設置級聯關系，不然對表操作時要先讀取一個類的數據，再將新建的一個類的數據添加到這個類上才成功對三張表同時操作。
2.2、Hibernate用註解方式實現一對多、多對多關系