Mybatis一对多关联查询详解

要点

在Student类中添加List<Classes> classList 属性
在Classes类中添加List<Student> students属性

在ClassesMapper.xml中

< resultMap>
…
< collection ofType="Student">
< /collection>
</ resultMap>

在StudentMapper.xml中
< resultMap>
…
< collection ofType="Classes">
< /collection>
</ resultMap>

1.创建数据表

本实例需要两张数据表
student表：

classes表

2.创建实体类

Student：

package com.ytsky.mybatis.demo.entity;import java.util.List;public class Student {private int id;private String stuno;private String stuname;private String sex;private String classno;private  List<Classes> classesList;public int getId() {return id;}public void setId(int id) {this.id = id;}public List<Classes> getClassesList() {return classesList;}public void setClassesList(List<Classes> classesList) {this.classesList = classesList;}public String getStuno() {return stuno;}public void setStuno(String stuno) {this.stuno = stuno;}public String getStuname() {return stuname;}public void setStuname(String stuname) {this.stuname = stuname;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public String getClassno() {return classno;}public void setClassno(String classno) {this.classno = classno;}@Overridepublic String toString() {return "Student{" +"id=" + id +", stuno='" + stuno + '\'' +", stuname='" + stuname + '\'' +", sex='" + sex + '\'' +", classno='" + classno + '\'' +", classesList=" + classesList +'}';}
}

Classes：

package com.ytsky.mybatis.demo.entity;import java.util.List;public class Classes {private int id;private String classno;private String name;private String major;private List<Student> students;public List<Student> getStudents() {return students;}public void setStudents(List<Student> students) {this.students = students;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getClassno() {return classno;}public void setClassno(String classno) {this.classno = classno;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getMajor() {return major;}public void setMajor(String major) {this.major = major;}@Overridepublic String toString() {return "Classes{" +"id=" + id +", classno='" + classno + '\'' +", name='" + name + '\'' +", major='" + major + '\'' +", students=" + students +'}';}
}

3.创建映射文件

ClassesMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.ytsky.mybatis.demo.dao.ClassesMapper"><select id="selectClassesWithStudent" resultMap="ClassesWithStudentMap">select classes.id, classes.classno, name, major,student.id, student.classno, stuno, sex, stunamefrom db_quote.classesjoin db_quote.studenton db_quote.student.id = db_quote.classes.idwhere db_quote.student.classno="Class001";</select><resultMap id="ClassesWithStudentMap" type="Classes"><id column="id" property="id" /><result column="classno" property="classno" /><result column="name" property="name" /><result column="major" property="major" /><collection property="students" ofType="Student"><id column="id" property="id" /><result column="classno" property="classno" /><result column="stuno" property="stuno" /><result column="sex" property="sex" /></collection></resultMap></mapper>

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.ytsky.mybatis.demo.dao.StudentMapper"><select id="selectStudentWithClasses" resultMap="StudentWithClassesMap">select student.id, stuno, stuname, sex, student.classno,classes.id, classes.classno,name, majorfrom db_quote.studentjoin db_quote.classeson classes.id = student.id;</select><resultMap id="StudentWithClassesMap" type="Student"><id column="id" property="id" /><result column="classno" property="classno" /><result column="stuno" property="stuno" /><result column="stuname" property="stuname" /><result column="sex" property="sex" /><collection property="classesList" ofType="Classes"><id column="id" property="id" /><result column="classno" property="classno" /><result column="name" property="name" /><result column="major" property="major" /></collection></resultMap></mapper>

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><properties resource="jdbc.properties"/><settings><setting name="mapUnderscoreToCamelCase" value="true"/><setting name="logImpl" value="LOG4J"/></settings>
<!--    <typeAliases>-->
<!--        <typeAlias type="com.ytsky.mybatis.demos.entity.Customer" alias="Customer"/>-->
<!--    </typeAliases>--><typeAliases><package name="com.ytsky.mybatis.demo.entity"/></typeAliases><plugins><plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin></plugins><environments default="dev"><environment id="dev"><transactionManager type="JDBC"></transactionManager><dataSource type="POOLED"><property name="driver" value="${jdbc.driver}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/><property name="url" value="${jdbc.url}"/></dataSource></environment></environments><mappers><mapper resource="mapper/CustomerMapper.xml"></mapper><mapper resource="mapper/ProductMapper.xml"></mapper><mapper resource="mapper/ProductTypeMapper.xml"></mapper><mapper resource="mapper/UserMapper.xml"></mapper><mapper resource="mapper/StudentMapper.xml"></mapper><mapper resource="mapper/ClassesMapper.xml"></mapper></mappers></configuration>

4.创建数据操作接口

ClassesMapper:

package com.ytsky.mybatis.demo.dao;import com.ytsky.mybatis.demo.entity.Classes;import java.util.List;public interface ClassesMapper {List<Classes> selectClassesWithStudent();
}

StudentMapper:

package com.ytsky.mybatis.demo.dao;import com.ytsky.mybatis.demo.entity.Student;import java.util.List;public interface StudentMapper {List<Student>selectStudentWithClasses();int updateById(Student student);
}

5.编写测试类

Test1：

package com.ytsky.mybatis.demo.test1;import com.ytsky.mybatis.demo.dao.ClassesMapper;
import com.ytsky.mybatis.demo.dao.StudentMapper;
import com.ytsky.mybatis.demo.entity.Classes;
import com.ytsky.mybatis.demo.entity.Student;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;
import java.util.List;public class Test1 {private static SqlSessionFactory factory;static {try{factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config.xml"));} catch (IOException e) {e.printStackTrace();}}public static void main(String[] args) {
//        System.out.println(findClassesWithStudent());System.out.println(findStudentWithClasses());}public static List<Classes> findClassesWithStudent(){SqlSession session = factory.openSession();List<Classes> classes = session.getMapper(ClassesMapper.class).selectClassesWithStudent();session.close();return classes;}public static List<Student> findStudentWithClasses(){SqlSession session = factory.openSession();List<Student> students = session.getMapper(StudentMapper.class).selectStudentWithClasses();session.close();return students ;}}

6.运行结果

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