Mybatis中一对多关联表查询
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2022-04-15 23:15:29
整体目录结构sql语句drop database if exists course;create database course;use course;create table if not exists student( id int primary key auto_increment comment '学号', name varchar(4) not null unique comment '姓名', sex char(1) not null comment...
整体目录结构
sql语句
drop database if exists course;
create database course;
use course;
create table if not exists student(
id int primary key auto_increment comment '学号',
name varchar(4) not null unique comment '姓名',
sex char(1) not null comment '性别',
classId int not null comment '班级',
foreign key(classId) references class(id)
);
create table if not exists class(
id int primary key auto_increment comment '班级id',
name varchar(4) not null unique comment '班级名称',
greadeYear datetime comment '毕业年份'
);
show tables;
insert into class(name,greadeYear) values
('计算机',now()),
('英语',now()),
('数学',now());
insert into student(name,sex,classId) values
('张三','男',1),
('李四','男',2),
('王五','男',3),
('黑凤梨','女',1);
实体类
model.classes
package model;
import java.sql.Timestamp;
import java.util.List;
/**
* ClassName:Class
* Package:model
* Description:
*
* @Date:2020/7/30 9:06
* @Author:DangWei
*/
public class Classes {
private Integer id;
private String name;
private Timestamp greadeYear;
private List<Student> students;
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Timestamp getGreadeYear() {
return greadeYear;
}
public void setGreadeYear(Timestamp greadeYear) {
this.greadeYear = greadeYear;
}
@Override
public String toString() {
return "Classes{" +
"id=" + id +
", name='" + name + '\'' +
", greadeYear=" + greadeYear +
", students=" + students +
'}';
}
}
model.Student
package model;
/**
* ClassName:User
* Package:model
* Description:
*
* @Date:2020/7/29 8:09
* @Author:DangWei
*/
public class Student {
private Integer id;
private String name;
private String sex;
private Integer classId;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Integer getClassId() {
return classId;
}
public void setClassId(Integer classId) {
this.classId = classId;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", classId=" + classId +
'}';
}
}
Dao接口
ClassesDao
package Dao;
import model.Classes;
import java.util.List;
/**
* ClassName:ClassDao
* Package:Dao
* Description:
*
* @Date:2020/7/30 9:29
* @Author:DangWei
*/
public interface ClassesDao {
List<Classes> selectClasses();
}
StudentDao
package Dao;
import model.Student;
import java.util.List;
/**
* ClassName:UserDAO
* Package:Dao
* Description:
*
* @Date:2020/7/29 8:10
* @Author:DangWei
*/
public interface StudentDao {
List<Student> selectStudent();
}
xml映射文件
ClassDao.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="Dao.ClassesDao">
<resultMap id="result" type="model.Classes">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="greadeYear" column="greadeYear"/>
</resultMap>
<resultMap id="student" type="model.Classes" extends="result">
<collection property="students" ofType="model.Student">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="sex" property="sex" />
<result column="classId" property="classId"/>
</collection>
</resultMap>
<select id="selectClasses" resultMap="student">
select * from class c join student s on c.id=s.classId
</select>
</mapper>
StudentDao.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="Dao.StudentDao">
<resultMap id="result" type="model.Student">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="sex" property="sex" />
<result column="classId" property="classId"/>
</resultMap>
<select id="selectStudent" resultMap="result">
select * from student
</select>
</mapper>
Mybatis-config.xml配置文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/course?characterEncoding=utf8"/>
<property name="username" value="root"/>
<property name="password" value=""/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="Dao/StudentDao.xml"/>
<mapper resource="Dao/ClassesDao.xml"/>
</mappers>
</configuration>
测试类
public class TestMybatis {
public static void main(String[] args) throws IOException {
InputStream inputStream= Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(inputStream);
SqlSession session=factory.openSession();
StudentDao studentDao=session.getMapper(StudentDao.class);
List<Student> students=studentDao.selectStudent();
for(Student student:students){
System.out.println(student);
}
System.out.println("==========================我是分割线==========================");
ClassesDao classesDao=session.getMapper(ClassesDao.class);
List<Classes> classesList=classesDao.selectClasses();
for(Classes item:classesList){
System.out.println(item);
}
}
}
输出结果
Student{id=1, name='张三', sex='男', classId=1}
Student{id=2, name='李四', sex='男', classId=2}
Student{id=3, name='王五', sex='男', classId=3}
Student{id=4, name='黑凤梨', sex='女', classId=1}
==========================我是分割线==========================
Classes{id=1, name='计算机', greadeYear=2020-07-30 09:00:06.0, students=[Student{id=1, name='计算机', sex='男', classId=1}]}
Classes{id=2, name='英语', greadeYear=2020-07-30 09:00:06.0, students=[Student{id=2, name='英语', sex='男', classId=2}]}
Classes{id=3, name='数学', greadeYear=2020-07-30 09:00:06.0, students=[Student{id=3, name='数学', sex='男', classId=3}]}
本文地址:https://blog.csdn.net/Mainhxj/article/details/107683341
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