三.Mybatis 多对一与一对多

 　　Profess.java  　　一方

package com.pojo;
//一对多 一方

import java.util.List;

public class Profess {
    int proid;
    String professName;
    List<Student> stus;
    public int getProid() {
        return proid;
    }
    public void setProid(int proid) {
        this.proid = proid;
    }
    public String getProfessName() {
        return professName;
    }
    public void setProfessName(String professName) {
        this.professName = professName;
    }
    public List<Student> getStus() {
        return stus;
    }
    public void setStus(List<Student> stus) {
        this.stus = stus;
    }
}

　　Student.java　　 多方

package com.pojo;

import java.util.Date;
//学员和专业  多对一 多方
public class Student {
    int stuid;
    String stuName;
    int stuAge;
    Date stuDate;
    String stuSex;
    String stuProfess;//专业外键字段，可以保留
    String status;
    String professName;//为了方便业务，补充一个专业名字的属性
    Profess profess;//专业对象，做级联查询
    
    public int getStuid() {
        return stuid;
    }
    public void setStuid(int stuid) {
        this.stuid = stuid;
    }
    public String getStuName() {
        return stuName;
    }
    public void setStuName(String stuName) {
        this.stuName = stuName;
    }
    public int getStuAge() {
        return stuAge;
    }
    public void setStuAge(int stuAge) {
        this.stuAge = stuAge;
    }
    public Date getStuDate() {
        return stuDate;
    }
    public void setStuDate(Date stuDate) {
        this.stuDate = stuDate;
    }
    public String getStuSex() {
        return stuSex;
    }
    public void setStuSex(String stuSex) {
        this.stuSex = stuSex;
    }
    public String getStuProfess() {
        return stuProfess;
    }
    public void setStuProfess(String stuProfess) {
        this.stuProfess = stuProfess;
    }
    public String getStatus() {
        return status;
    }
    public void setStatus(String status) {
        this.status = status;
    }
    public String getProfessName() {
        return professName;
    }
    public void setProfessName(String professName) {
        this.professName = professName;
    }
    public Profess getProfess() {
        return profess;
    }
    public void setProfess(Profess profess) {
        this.profess = profess;
    }
}

　　IStudentDAO.java

package com.dao;

import java.util.List;

import com.pojo.Student;

public interface IStudentDAO {
    
    List<Student> getStuByProId(int proid);
    
    List<Student> manyToOne();
}

　　Student.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="com.dao.IStudentDAO">
<!--     学员和专业的多对一映射 -->
    <resultMap type="com.pojo.Student" id="stu_profess">
        <id property="stuid" column="stuid"/>
        <result property="stuName" column="stuName"/>
        <result property="stuAge" column="stuAge"/>
        <result property="stuDate" column="stuDate"/>
        <result property="stuSex" column="stuSex"/>
        <result property="stuProfess" column="stuProfess"/>
        <!--多对一 -->
        <association property="profess" javaType="com.pojo.Profess">
            <id property="proid" column="proid"></id>
            <result property="professName" column="professName"/>
        </association>
    </resultMap>
    
<!--     根据专业id来查询学员 -->
    <select id="getStuByProId" parameterType="int" resultType="com.pojo.Student">
        select * from student where stuprofess=#{id}
    </select>    
<!--     多对一的查询，查询学员同时查出专业信息 -->
    <select id="manyToOne" resultMap="stu_profess">
        select * from student a,profess b where a.stuProfess=b.proid
    </select>
</mapper>

IProfessDAO.java

package com.dao;

import java.util.List;

import com.pojo.Profess;

public interface IProfessDAO {
    List<Profess> ontToMany();
}

　　Profess.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">
<!-- 一对多的映射 -->
<mapper namespace="com.dao.IProfessDAO">
    <resultMap id="pro_stu" type="com.pojo.Profess">
        <id property="proid" column="proid"></id>
        <result property="professName" column="professName"></result>
        <collection property="stus" ofType="com.pojo.Student" column="proid" select="com.dao.IStudentDAO.getStuByProId"></collection>
    </resultMap>
    
<!--     一对多的查询 -->
    <select id="ontToMany" resultMap="pro_stu">
        select * from profess
    </select>
</mapper>

多对一测试代码：

Test.java

package com.pojo;

import java.io.IOException;
import java.io.Reader;
import java.util.Date;
import java.util.List;

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 com.dao.IStudentDAO;

public class Test {
    public static void main(String[] args) throws IOException {
        //读取核心的配置文件
        Reader reader = Resources.getResourceAsReader("Configuration.xml");
        //创建会话工厂
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
        //数据库会话
        SqlSession session = factory.openSession();
        //查询一个对象  第一个参数字符串是由Student.xml 中的namespace+id组成
//        Student stu = session.selectOne("com.dao.StudentMapper.getStudentById",5);
        
        //通过接口的方式
        IStudentDAO stuDAO = session.getMapper(IStudentDAO.class);
        
        //测试多对一的级联查询
        List<Student> list = stuDAO.manyToOne();
        for (Student stu : list) {
            System.out.println(stu.getStuName()+"\t"+stu.getProfess().getProfessName());
        }
        
        session.close();
    }
}

一对多测试代码：

package com.pojo;

import java.io.IOException;
import java.io.Reader;
import java.util.Date;
import java.util.List;

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 com.dao.IProfessDAO;
import com.dao.IStudentDAO;

public class Test {
    public static void main(String[] args) throws IOException {
        //读取核心的配置文件
        Reader reader = Resources.getResourceAsReader("Configuration.xml");
        //创建会话工厂
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
        //数据库会话
        SqlSession session = factory.openSession();
        //查询一个对象  第一个参数字符串是由Student.xml 中的namespace+id组成
//        Student stu = session.selectOne("com.dao.StudentMapper.getStudentById",5);
        
        //通过接口的方式
        IStudentDAO stuDAO = session.getMapper(IStudentDAO.class);
        IProfessDAO proDAO = session.getMapper(IProfessDAO.class);

        //测试一对多查询
        List<Profess> list = proDAO.ontToMany();
        for (Profess pro : list) {
            System.out.println(pro.getProfessName());
            for (Student stu : pro.getStus()) {
                System.out.print(stu.getStuName()+"\t");
            }
            System.out.println();
        }
        session.close();
    }
}

Configuration中的注册

<!--     对象的映射文件注册 -->
    <mappers>
        <mapper resource="com/pojo/Student.xml"></mapper>
        <mapper resource="com/pojo/Profess.xml"></mapper>
    </mappers>