Spring 多对多

Posted 2022-04-06 hzyhx

多对多特点：建表只建了两个，但再数据库里就会产生三张表

 

第一步：创建一个Spring Starter Project工程 

          注意：这里创建和以前创建Spring Starter Project工程一样，但要添加驱动不一样，这里只添加了Spring Boot DevTools和 Spring Data JPA驱动

                 

第二步：添加配置文件

               （1）pom.xml的添加以下代码

                        1 <maven-jar-plugin.version>3.1.1</maven-jar-plugin.version> 

添加位置，如下图

                         

                    再在pom.xml中的<dependencies>标签中添加以下代码       

                       

1  <dependency>
2             <groupId>mysql</groupId>
3             <artifactId>mysql-connector-java</artifactId>
4             <version>5.1.38</version>
5         </dependency>

添加位置如下图

（2）配置此文件application.properties 添加以下代码    

 1 spring.datasource.driver-class-name=com.mysql.jdbc.Driver
 2            spring.datasource.url=jdbc:mysql://localhost:3306/testdb?useUnicode=true&characterEncoding=UTF-8//将testdb改成自己的数据库名
 3            spring.datasource.username=testdb  //自己的数据库名
 4            spring.datasource.password=testdb //自己的数据库密码
 5 
 6            spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialect
 7            spring.jpa.hibernate.ddl-auto = update//自动创建表
 8 
 9            logging.level.org.hibernate.SQL=DEBUG
10            logging.level.org.hibernate.type=TRACE

注意：连接数据库的时候，记得连自己的 

(3)在/src/main/java中的配置(config)包，添加扫描包 ，添加以下代码

1 //Spring Boot应用
2 @SpringBootApplication
3 //@EnableJpaRepositories启用JPA存储库
4 @EnableJpaRepositories(basePackages = "com.hzy.dao")
5 //@EntityScan实体扫描
6 @EntityScan(basePackages = "com.hzy.entity")

注意：要扫描的包写成自己的包名。 

假如：你的dao包名叫：com.xxx.dao；你的实体包叫：com.xxx.entity,
则你应该将com.hzy.dao改成com.xxx.dao；com.hzy.entity改成com.xxx.entity

 

第三步：再/src/main/java目录下建一个dao包和一个实体(entity)包，如图

               

第四步：在实体包中建一个Student实体类和一个Course实体类 

  多对多重要代码：

 1 //@ManyToMany多对多
 2       //cascade = CascadeType.ALL 级联关系=拥有以上所有级联操作权限
 3     @ManyToMany(cascade = CascadeType.ALL)
 4     
 5     /**
 6       *@JoinTable 关联表 *
 7       *name = "student_has_course" 关联表名 
 8       *joinColumns = @JoinColumn(name = "course_id", referencedColumnName = "id") 维护端外键 
 9       *inverseJoinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id") 被维护端外键 */
10     @JoinTable(name = "student_has_course", joinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "course_id", referencedColumnName = "id"))

 

Student实体类，代码如下：     

 1 package com.hzy.entity;
 2 
 3 import java.io.Serializable;
 4 import java.util.Set;
 5 
 6 import javax.persistence.CascadeType;
 7 import javax.persistence.Entity;
 8 import javax.persistence.GeneratedValue;
 9 import javax.persistence.GenerationType;
10 import javax.persistence.Id;
11 import javax.persistence.JoinTable;
12 import javax.persistence.ManyToMany;
13 import javax.persistence.Table;
14 import javax.persistence.JoinColumn;
15 
16 @Entity//实体
17 @Table(name="student")/**@Table表  (name="student")数据库里的表名*/
18 public class Student implements Serializable 
19 
20     private static final long serialVersionUID = 5464805301818181901L;
21 
22     @Id
23     @GeneratedValue(strategy=GenerationType.IDENTITY)
24     private int id;
25     
26     private String name;
27     
28     //@ManyToMany多对多
29     //cascade = CascadeType.ALL 级联关系=拥有以上所有级联操作权限
30     @ManyToMany(cascade = CascadeType.ALL)
31     
32     /**
33       *@JoinTable 关联表 *
34       *name = "student_has_course" 关联表名 
35       *joinColumns = @JoinColumn(name = "course_id", referencedColumnName = "id") 维护端外键 
36       *inverseJoinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id") 被维护端外键 */
37     @JoinTable(name = "student_has_course", joinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "course_id", referencedColumnName = "id"))
38     
39   //这里表示一个学生可以有多门课程，知识用到了集合Set<T>
40     private Set<Course> course;
41     
42     public Student() 
43         
44     
45     
46     public Student(String name) 
47         super();
48         this.name=name;
49     
50 
51     public int getId() 
52         return id;
53     
54 
55     public void setId(int id) 
56         this.id = id;
57     
58 
59     public String getName() 
60         return name;
61     
62 
63     public void setName(String name) 
64         this.name = name;
65     
66 
67     public Set<Course> getCourse() 
68         return course;
69     
70 
71     public void setCourse(Set<Course> course) 
72         this.course = course;
73     
74 
75     @Override
76     public String toString() 
77         return "Student [id=" + id + ", name=" + name + ",course="+ course +"]";
78     
79     
80     
81     
82 

 

Course实体类，代码如下：

 1 package com.hzy.entity;
 2 
 3 import java.io.Serializable;
 4 import java.util.Set;
 5 
 6 import javax.persistence.CascadeType;
 7 import javax.persistence.Entity;
 8 import javax.persistence.GeneratedValue;
 9 import javax.persistence.GenerationType;
10 import javax.persistence.Id;
11 import javax.persistence.JoinTable;
12 import javax.persistence.ManyToMany;
13 import javax.persistence.Table;
14 import javax.persistence.JoinColumn;
15 
16 @Entity//实体
17 @Table(name = "course")//@Table添加表   name = "course"表名
18 public class Course implements Serializable 
19 
20     private static final long serialVersionUID = -35542463820821380L;
21     
22     
23     @Id
24     @GeneratedValue(strategy = GenerationType.IDENTITY)
25     private int id;
26     
27     private String name;
28     
29     //@ManyToMany多对多
30     //cascade = CascadeType.ALL 级联关系=拥有以上所有级联操作权限
31     @ManyToMany(cascade = CascadeType.ALL)
32     
33     /**
34       *@JoinTable 关联表 *
35       *name = "student_has_course" 关联表名 
36       *joinColumns = @JoinColumn(name = "course_id", referencedColumnName = "id") 维护端外键 
37       *inverseJoinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id") 被维护端外键 */
38     @JoinTable(name = "student_has_course", joinColumns = @JoinColumn(name = "course_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id"))
39     
40     //这里表示一个学生可以有多门课程，知识用到了集合Set<T>
41     private Set<Student> student;
42 
43     public Course() 
44     
45 
46     public Course(String name) 
47         super();
48         this.name = name;
49     
50 
51     public int getId() 
52         return id;
53     
54 
55     public void setId(int id) 
56         this.id = id;
57     
58 
59     public String getName() 
60         return name;
61     
62 
63     public void setName(String name) 
64         this.name = name;
65     
66 
67     public Set<Student> getStudent() 
68         return student;
69     
70 
71     public void setStudent(Set<Student> student) 
72         this.student = student;
73     
74 
75     @Override
76     public String toString() 
77         return "Course [id=" + id + ", name=" + name + ", student=" + student + "]";
78     
79     
80     
81 
82 

 

第五步：在dao包中建一个StudentRepository和CourseRepository类

             StudentRepository类，代码如下：                      

 1 package com.hzy.dao;
 2 
 3 import org.springframework.data.jpa.repository.JpaRepository;
 4 import org.springframework.stereotype.Repository;
 5 
 6 import com.hzy.entity.Student;
 7 
 8 @Repository
 9 public interface StudentRepository extends JpaRepository<Student, Integer> 
10 
11 

 

CourseRepository类，代码如下：

 1 package com.hzy.dao;
 2 
 3 import org.springframework.data.jpa.repository.JpaRepository;
 4 import org.springframework.stereotype.Repository;
 5 
 6 import com.hzy.entity.Course;
 7 
 8 
 9 @Repository
10 public interface CourseRepository extends JpaRepository<Course, Integer> 
11 
12 
13 

第六步：在config配置文件中 进行实例化student和course实体类

            完整的config配置文件代码，如下：

             

 1 package com.hzy.config;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 import org.springframework.beans.factory.annotation.Autowired;
 7 import org.springframework.boot.CommandLineRunner;
 8 import org.springframework.boot.SpringApplication;
 9 import org.springframework.boot.autoconfigure.SpringBootApplication;
10 import org.springframework.boot.autoconfigure.domain.EntityScan;
11 import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
12 
13 import com.hzy.dao.CourseRepository;
14 import com.hzy.dao.StudentRepository;
15 import com.hzy.entity.Course;
16 import com.hzy.entity.Student;
17 
18 @SpringBootApplication
19 @EnableJpaRepositories(basePackages = "com.hzy.dao")
20 @EntityScan(basePackages = "com.hzy.entity")
21 public class HibernateManyToManyMappingApplication implements CommandLineRunner 
22 
23     @Autowired
24     private StudentRepository studentRepository;
25     
26     
27     @Autowired
28     private CourseRepository courseRepository;
29     
30     public static void main(String[] args) 
31         SpringApplication.run(HibernateManyToManyMappingApplication.class, args);
32     
33 
34     @Override
35     public void run(String... args) throws Exception 
36         
37         Student JackSon = new Student("易烊千玺");
38         Student wy = new Student("王源");
39         
40         Course dance = new Course("跳舞");
41         Course sing = new Course("跳舞");
42         Course perform = new Course("跳舞");
43         
44         //将所有的功课放到set<>集合中
45         Set<Course> sets = new HashSet<>();
46         //将跳舞、跳舞、跳舞添加到集合里
47         sets.add(dance);
48         sets.add(sing);
49         sets.add(perform);
50         
51         //再用JackSon学生调用刚放到集合里的功课
52         JackSon.setCourse(sets);
53         
54         Set<Course> sets2 = new HashSet<>();
55         sets2.add(dance);
56         sets2.add(sing);
57         
58         wy.setCourse(sets2);
59         
60         //再将JackSon学和JackSon的功课保存到StudentRepository中
61         studentRepository.save(JackSon);
62     
63 
64 

第七步：运行