mybatis 一对多

学科

package cn.itcast.javaee.mybatis.one2many;

import java.util.ArrayList;
import java.util.List;

/**
 * 学科(单方)
 * @author AdminTC
 */
public class Grade {
    private Integer id;
    private String name;
    private List<Student> studentList = new ArrayList<Student>();//关联属性
    public Grade(){}
    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 List<Student> getStudentList() {
        return studentList;
    }
    public void setStudentList(List<Student> studentList) {
        this.studentList = studentList;
    }
}

学生

package cn.itcast.javaee.mybatis.one2many;

/**
 * 学生(多方)
 * @author AdminTC
 */
public class Student {
    private Integer id;
    private String name;
    private Grade grade;//关联属性
    public Student(){}
    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 Grade getGrade() {
        return grade;
    }
    public void setGrade(Grade grade) {
        this.grade = grade;
    }
}

GradeMapper.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="gradeNamespace">
    
    <resultMap type="cn.itcast.javaee.mybatis.one2many.Grade" id="gradeMap">
        <id property="id" column="gid"/>
        <result property="name" column="gname"/>
    </resultMap>    
    
    
    
    <!-- 查询哈哈是哪个学科的 -->
    <select id="findByName" parameterType="string" resultMap="gradeMap">
        select g.gname
        from students s inner join grades g
        on s.sgid = g.gid
        and s.sname = #{xxxxx}
    </select>
    
    
</mapper>

StudentMapper.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="studentNamespace">
    
    <resultMap type="cn.itcast.javaee.mybatis.one2many.Student" id="studentMap">
        <id property="id" column="sid"/>
        <result property="name" column="sname"/>
    </resultMap>    
    
    
    <!-- 查询java学科有哪些学生信息 -->
    <select id="findAllByName" parameterType="string" resultMap="studentMap">
        select s.sid,s.sname
        from students s inner join grades g
        on s.sgid = g.gid
        and g.gname = #{name}
    </select>
    
</mapper>

GradeStudentDao

package cn.itcast.javaee.mybatis.one2many;

import java.util.List;

import org.apache.ibatis.session.SqlSession;

import cn.itcast.javaee.mybatis.util.MybatisUtil;

/**
 * 持久层
 * @author AdminTC
 */
public class GradeStudentDao {
    /**
     * 查询java学科有哪些学生信息
     * @param name 表示学科名
     */
    public List<Student> findAllByName(String name) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            return sqlSession.selectList("studentNamespace.findAllByName",name);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    
    /**
     * 查询哈哈是哪个学科的
     * @param name 表示学生姓名
     */
    public Grade findByName(String name) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            return sqlSession.selectOne("gradeNamespace.findByName",name);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    
    
    
    
    
    public static void main(String[] args) throws Exception{
        GradeStudentDao dao = new GradeStudentDao();
        List<Student> studentList = dao.findAllByName("java");
        System.out.println("java学科有"+studentList.size()+"个学生，它们信息如下：");
        for(Student s : studentList){
            System.out.println(s.getId()+":"+s.getName());
        }
        System.out.println("-----------------------------------------------------------");
        Grade grade = dao.findByName("哈哈");
        System.out.println("哈哈是"+grade.getName()+"学科的");
        System.out.println("-----------------------------------------------------------");
        grade = dao.findByName("呵呵");
        System.out.println("呵呵是"+grade.getName()+"学科的");
    }
}