Jpa配置一对多关系
作者：互联网
在网上查了很多关于jpa的一对多表关联的操作,踩了很多坑,今天终于解决了
下面上一下我自己的代码,记录一下
老师和学生(一对多关系)
首先搭建环境,添加依赖包
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.lyf</groupId>
<artifactId>one-to-more</artifactId>
<version>1.0-SNAPSHOT</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.3.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.22</version>
</dependency>
</dependencies>
</project>
编写数据库配置文件
spring.datasource.url=jdbc:mysql://localhost:3306/jpa?serverTimezone=UTC spring.datasource.username=root spring.datasource.password=08186912 spring.datasource.driver-class-name=com.mysql.jdbc.Driver spring.jpa.hibernate.ddl-auto=update spring.jpa.show-sql=true spring.jpa.database=mysql
实体类
package com.lyf.pojo;
import lombok.Data;
import javax.persistence.*;
/**
* @Date：2019-04-12
* @Description：com.lyf.pojo
* @version：1.0
*/
@Data
@Entity
@Table(name = "tb_student")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "s_id")
private Long sId;
@Column(name = "s_name")
private String sName;
/**
* 多个学生对应一个老师
* 注解形式配置多对一
* 1,配置表关系
* 2,配置外键
*/
@ManyToOne(targetEntity = Teacher.class)
@JoinColumn(name = "s_t_id",referencedColumnName = "t_id")
private Teacher teacher;
}
package com.lyf.pojo;
import lombok.Data;
import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;
/**
* @Date：2019-04-12
* @Description：教师和学生是一对多
*/
@Data
@Entity
@Table(name = "tb_teacher")
public class Teacher {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "t_id")
private Long tId;
@Column(name = "t_name")
private String tName;
//配置老师和学生一对多
/**
* 注解配置多表关系
* 1,声名关系
* 2,配置外键,或者中间表
* OneToMany配置一对多
* targetEntity设置对应的实体类的类型
* JoinColumn 配置外键
* name:外键的名称,
* referencedColumnName参照的主表的主键字段名称
*/
@OneToMany(targetEntity = Student.class)
@JoinColumn(name = "s_t_id",referencedColumnName = "t_id")
private Set<Student> students = new HashSet<>();
}
springboot启动类(引导类)
package com.lyf;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
/**
* @Date：2019-04-12
* @Description：com.lyf
* @version：1.0
*/
@SpringBootApplication
public class App {
public static void main(String[] args) {
SpringApplication.run(App.class,args);
}
}
启动引导类,查看数据库会发现表生成成功
dao层代码就不上了,继承JpaRepository就行了
接下来我们进行保存操作
package com.lyf;
import com.lyf.dao.StudentDao;
import com.lyf.dao.TeacherDao;
import com.lyf.pojo.Student;
import com.lyf.pojo.Teacher;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
/**
* @Date：2019-04-12
* @Description：com.lyf
* @version：1.0
*/
@SpringBootTest
@RunWith(SpringRunner.class)
public class OneToMoreTest {
@Autowired
private TeacherDao teacherDao;
@Autowired
private StudentDao studentDao;
@Test
public void addTest(){
Student student = new Student();
student.setSName("老篮孩i");
Teacher teacher = new Teacher();
teacher.setTName("刘老师");
//关联学生和老师,添加学生信息时，还需添加外键的值
student.setTeacher(teacher);
studentDao.save(student);
teacherDao.save(teacher);
}
}
结果报错了,发现我是先保存的学生信息，再保存的老师信息,此时数据库中并没有老师的信息,给学生关联老师信息肯定是有问题的
报错信息
org.springframework.dao.InvalidDataAccessApiUsageException:
org.hibernate.TransientPropertyValueException:
object references an unsaved transient instance - save the transient instance before flushing : com.lyf.pojo.Student.teacher -> com.lyf.pojo.Teacher;
nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException:
object references an unsaved transient instance - save the transient instance before flushing :
com.lyf.pojo.Student.teacher -> com.lyf.pojo.Teacher
学生表记录插入了,老师表是空的
改成
package com.lyf;
import com.lyf.dao.StudentDao;
import com.lyf.dao.TeacherDao;
import com.lyf.pojo.Student;
import com.lyf.pojo.Teacher;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
/**
* @Date：2019-04-12
* @Description：com.lyf
* @version：1.0
*/
@SpringBootTest
@RunWith(SpringRunner.class)
public class OneToMoreTest {
@Autowired
private TeacherDao teacherDao;
@Autowired
private StudentDao studentDao;
@Test
public void addTest(){
Student student = new Student();
student.setSName("老篮孩i");
Teacher teacher = new Teacher();
teacher.setTName("刘老师");
//关联学生和老师,添加学生信息时，还需添加外键的值
student.setTeacher(teacher);
//要先保存主表信息
teacherDao.save(teacher);
studentDao.save(student);
}
}
控制台信息,很显然成功了
Hibernate: alter table tb_student add constraint FKsojy7bicq68v21slcq9mtwtou foreign key (s_t_id) references tb_teacher (t_id) 2019-04-12 23:29:42.036 INFO 10980 --- [ main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default' 2019-04-12 23:29:42.748 INFO 10980 --- [ main] com.lyf.OneToMoreTest : Started OneToMoreTest in 7.77 seconds (JVM running for 9.806) Hibernate: insert into tb_teacher (t_name) values (?) Hibernate: insert into tb_student (s_name, s_t_id) values (?, ?)
查看数据库也没有问题
暂时先写到这,这偏博客会持续更新
标签：name,Jpa,配置,lyf,org,import,一对,com,teacher 来源： https://www.cnblogs.com/a-small-lyf/p/10699326.html