MyBatis 一对多关联查询

sqlxml文件

<?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="ClassStudent">



    <!-- 1.联表查询SELECT * from class c ,teacher t where c.t_id = t.t_id and c.c_id=1 -->

    <select id="getClass" parameterType="int" resultMap="getClassMap">

        SELECT *

        from class c

        ,student s where c.c_id = s.c_id and c.c_id = #{id}

    </select>

    <resultMap type="com.stone.bean.ClassT" id="getClassMap">

        <id property="id" column="c_id" />

        <result property="name" column="c_name" />

        <collection property="list" ofType="com.stone.bean.Student">

            <id property="id" column="s_id" />

            <result property="name" column="s_name" />

        </collection>

    </resultMap>

    <!-- 2.查询两次select * from class where c_id = 1 ; SELECT * from teacher where 

        t_id = 1 -->



    <select id="getClass2" resultMap="getClass2Map">

        select * from class where c_id

        =#{id}

    </select>

    <select id="getTeacher" parameterType="int" resultType="com.stone.bean.Teacher">

        select

        t_id id,t_name name

        from teacher where t_id=#{id}

    </select>

    <select id="getStudents" parameterType="int" resultType="com.stone.bean.Student">

        select

        S_id id,s_name name from student where c_id=#{id}

    </select>

    <resultMap type="com.stone.bean.ClassT" id="getClass2Map">

        <id property="id" column="c_id" />

        <result property="name" column="c_name" />

        <association property="teacher" column="t_id" select="getTeacher">

        </association>

        <collection property="list" column="c_id" select="getStudents"></collection>

    </resultMap>

　　<!--collection 可以进行嵌套-->
　　<resultMap type="person" id="selectMulti" extends="BaseResultMap">
　　　　<collection property="orderList" ofType="Orders">
　　　　　　<id ...>
　　　　　　<result ...>
　　　　　　<collection property="detailList" ofType="OrderDetail">
　　　　　　　　<id ...>
　　　　　　　　<result ...>
　　　　　　</collection>
　　　　</collection>
　　</resultMap>


</mapper>

 

javabean

package com.stone.bean;



import java.util.List;



public class ClassT {



    private int id;

    private String name;

    private Teacher teacher;

    private List<Student> list;

    

    

    public ClassT(int id, String name, Teacher teacher) {

        super();

        this.id = id;

        this.name = name;

        this.teacher = teacher;

    }

    public ClassT() {

        super();

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Teacher getTeacher() {

        return teacher;

    }

    public void setTeacher(Teacher teacher) {

        this.teacher = teacher;

    }

    @Override

    public String toString() {

        return "ClassT [id=" + id + ", name=" + name + ", teacher=" + teacher

                + ", list=" + list + "]";

    }

    public List<Student> getList() {

        return list;

    }

    public void setList(List<Student> list) {

        this.list = list;

    }



    

}

package com.stone.bean;



public class Student {



    private int id;

    private String name;

    public Student(int id, String name) {

        super();

        this.id = id;

        this.name = name;

    }

    public Student() {

        super();

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "Student [id=" + id + ", name=" + name + "]";

    }

    

}

package com.stone.bean;



public class Teacher {

    private int id;

    private String name;

    public Teacher(int id, String name) {

        super();

        this.id = id;

        this.name = name;

    }

    public Teacher() {

        super();

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "Teacher [id=" + id + ", name=" + name + "]";

    }

    

}

 

test

package com.stone.dao;



import org.apache.ibatis.session.SqlSession;



import com.stone.bean.ClassT;

import com.stone.db.DBAccess;



public class DBDaoClassStudent {



    public static void main(String[] args) {

        DBAccess dbAccess = new DBAccess();

        SqlSession sqlSession = null;

        try {

            sqlSession = dbAccess.getSqlSession();

            String statement = "ClassStudent.getClass";

            Object parameter = 1;

            // 通过sqlSession执行SQL语句；

            ClassT class1 = sqlSession.selectOne(statement, parameter);

            System.out.println(class1);

            System.out.println("=======================");

            statement = "ClassStudent.getClass2";

            ClassT class2 = sqlSession.selectOne(statement, parameter);

            System.out.println(class2);



        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            if (sqlSession != null) {

                sqlSession.close();

            }

        }

    }



}