SSM(二)MyBatis多表聯查

 

這篇文章寫了以下幾個簡單的例子，用來說明MyBatis多標聯查基本語法

1.sql片段的用法

2.一對多查詢

3.多條sql的一對多查詢

4.多對一查詢

5.多條sql一對多查詢

6、多對多查詢

這里沿着接口→小配置的路線寫了，測試類就是遍歷輸出結果:

一、接口：

package cn.sohappy.acourses.course0921;

import cn.sohappy.acourses.bean.BillManyToOne;
import cn.sohappy.acourses.bean.UserOneToMany;
import cn.sohappy.bean.Smbms_user;

import java.util.List;

public interface IUserDAO {
    //01.sql片段,查詢所有user
    List<Smbms_user> findAll();
    //02.oneToMany，傳入user，返回包含賬單信息的user
    UserOneToMany getUserOneToManyBills(UserOneToMany user);
    //03.oneToMany，多條sql查詢，傳入user，返回包含賬單信息的user
    UserOneToMany getUserOneToManyBillsMultiSQL(UserOneToMany user);
    //04.manyToOne,傳入bill,返回包含用戶信息的bill
    BillManyToOne getBillManyToOneUser(BillManyToOne bill);
    //05.manyToOne,多條sql查詢，傳入bill,返回包含用戶信息的bill
    BillManyToOne getBillManyToOneUserMultiSQL(BillManyToOne bill);
}

二、小配置

先實現第一個方法

1、List<Smbms_user> findAll();查詢所有user的編號，名字，密碼

小配置的配置頭

 

<?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="cn.sohappy.acourses.course0921.IUserDAO">
    <!--此處是代碼-->
</mapper>

 

以下省略配置頭

 

 

　　<sql id="columns">
        userCode,userName,userPassword
    </sql>
    <resultMap id="mUser" type="cn.sohappy.bean.Smbms_user" autoMapping="false">
        <id property="username" column="userName"/>
        <result property="userpassword" column="userPassword"/>
        <result property="usercode" column="userCode"/>
    </resultMap>
    <!--用<include refid="columns"/>代替*-->
    <select id="findAll" resultMap="mUser">
        select <include refid="columns"/> from smbms_user
    </select>

 

2、UserOneToMany getUserOneToManyBills(UserOneToMany user);

查詢某個用戶的賬單信息，首先將賬單List植入用戶類中(第11行)

 

package cn.sohappy.acourses.bean;

import java.util.List;

public class UserOneToMany {
    private Long id;
    private String usercode;
    private String username;

    //a user has lots of bills
    private List<BillManyToOne> bills;

    //getter and setter
}

 

小配置代碼：

resultMap中property是對象的屬性名，column是數據表中的字段名。collection是UserOneToMany對象中植入的泛型集合屬性List<BillManyToOne> bills

語法是：<collection property="bills" ofType="cn.sohappy.acourses.bean.BillManyToOne">...code...</collection>

<!--02.oneToMany-->
    <resultMap id="UserOneToManyBills" type="cn.sohappy.acourses.bean.UserOneToMany" autoMapping="false">
        <id property="id" column="u_id"/>
        <result property="username" column="userName"/>
        <collection property="bills" ofType="cn.sohappy.acourses.bean.BillManyToOne">
            <id property="id" column="b_id"/>
            <result property="productname" column="productName"/>
            <result property="billcode" column="billCode"/>
        </collection>
    </resultMap>
    <select id="getUserOneToManyBills" resultMap="UserOneToManyBills">
        <!--不好，id重名了，起個別名吧-->
        select smbms_user.id as u_id,userName,smbms_bill.id as b_id,productName,billCode from smbms_user,smbms_bill
        where smbms_user.id=smbms_bill.createdBy and userCode=#{usercode}
    </select>

3、UserOneToMany getUserOneToManyBillsMultiSQL(UserOneToMany user);

該方法通過多條sql查詢user和其賬單

小配置代碼：其中#{**}是占位符

<!--03.oneToMany多條sql-->
    <resultMap id="UserOneToManyBillsMultiSQL" type="cn.sohappy.acourses.bean.UserOneToMany" autoMapping="false">
        <id property="id" column="id"/>
        <result property="username" column="userName"/>
        <!--下行的select為第二條sql名,column為第一條sql的字段名，其唯一值作為第二條sql的條件-->
        <collection property="bills" ofType="cn.sohappy.acourses.bean.BillManyToOne" select="selectBillsByUser" column="id"/>
    </resultMap>
    <select id="selectBillsByUser" resultType="cn.sohappy.acourses.bean.BillManyToOne">
        select * from smbms_bill where createdBy=#{**}
    </select>
    <select id="getUserOneToManyBillsMultiSQL" resultMap="UserOneToManyBillsMultiSQL">
        select * from smbms_user where userCode=#{usercode}
    </select>

4、BillManyToOne getBillManyToOneUser(BillManyToOne bill);

傳入bill,返回包含用戶信息的bill，這里需要在bill類中植入user屬性及相應getter and setter：private UserOneToMany user;

 小配置代碼：這里使用的語法是：<association property="user" javaType="cn.sohappy.acourses.bean.UserOneToMany">...code...</association>

<!--04.manyToOne-->
    <resultMap id="BillManyToOneUser" type="cn.sohappy.acourses.bean.BillManyToOne" autoMapping="false">
        <id property="id" column="b_id"/>
        <result property="billcode" column="billCode"/>
        <association property="user" javaType="cn.sohappy.acourses.bean.UserOneToMany">
            <id property="id" column="u_id"/>
            <result property="usercode" column="userCode"/>
            <result property="username" column="userName"/>
        </association>
    </resultMap>
    <select id="getBillManyToOneUser" resultMap="BillManyToOneUser">
        select smbms_user.id as u_id,userCode,userName,smbms_bill.id as b_id,billCode from smbms_user,smbms_bill
        where smbms_user.id=smbms_bill.createdBy and billCode=#{billcode}
    </select>

5.BillManyToOne getBillManyToOneUserMultiSQL(BillManyToOne bill);多條sql多對一查詢

小配置代碼：

<!--05.manyToOne多條sql-->
    <resultMap id="BillManyToOneUserMultiSQL" type="cn.sohappy.acourses.bean.BillManyToOne" autoMapping="false">
        <id property="id" column="id"/>
        <result property="billcode" column="billCode"/>
        <association property="user" javaType="cn.sohappy.acourses.bean.UserOneToMany" autoMapping="false" select="selectUserByCreatedBy" column="CreatedBy">
            <id property="id" column="id"/>
            <result property="usercode" column="userCode"/>
            <result property="username" column="userName"/>
        </association>
    </resultMap>
    <select id="selectUserByCreatedBy" resultType="cn.sohappy.acourses.bean.UserOneToMany">
        select * from smbms_user where id=#{**}
    </select>
    <!--這里需要查找公共字段createdBy作為association中的column參數-->
    <select id="getBillManyToOneUserMultiSQL" resultMap="BillManyToOneUserMultiSQL">
        select id,billCode,createdBy from smbms_bill where billCode=#{billcode}
    </select>

最后寫下多對多查詢

其實多對多查詢和一對多查詢是一樣的，只不過表中可能沒有公共字段，要借助第三張表。

舉個例子：根據老師id查詢他所教授學生的id

下面建立三張表：

這是student表

這是老師表

這是第三張表

步驟和一對多是一樣的，先生成實體類，然后在老師中植入學生List

創建接口，寫個方法：

package cn.sohappy.acourses.course0923;

import cn.sohappy.acourses.bean.Teachert14;

public interface ITeacherDAO {
    Teachert14 findStudentsByTeacher(Teachert14 teacher);
}

 下面直接寫小配置了：

<?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="cn.sohappy.acourses.course0923.ITeacherDAO">
    <resultMap id="mTeacher" type="cn.sohappy.acourses.bean.Teachert14">
        <id property="tid" column="tid"/>
        <result property="tname" column="tname"/>
        <collection property="studentt14s" ofType="cn.sohappy.acourses.bean.Studentt14">
            <id property="sid" column="sid"/>
            <result property="sname" column="sname"/>
        </collection>
    </resultMap>
    <select id="findStudentsByTeacher" resultMap="mTeacher">
        select studentt14.sid,sname,teachert14.tid,tname from studentt14,teachert14,teacher_studentt14
        where studentt14.sid=teacher_studentt14.sid and teachert14.tid=teacher_studentt14.tid
        and teachert14.tid=#{tid}
    </select>
</mapper>

最后附上測試類和MyBatis工具類：

測試類：

package cn.test;

import cn.sohappy.acourses.bean.Studentt14;
import cn.sohappy.acourses.bean.Teachert14;
import cn.sohappy.acourses.course0923.ITeacherDAO;
import cn.sohappy.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

public class test20170923 {
    //多對多，借助第三張表
    @Test
    public void findStudentsByTeacher(){
        SqlSession session = MyBatisUtil.getSession();
        ITeacherDAO mapper = session.getMapper(ITeacherDAO.class);
        Teachert14 teachert14 = new Teachert14();
        teachert14.setTid(1L);
        Teachert14 teacher = mapper.findStudentsByTeacher(teachert14);
        for (Studentt14 item:teacher.getStudentt14s()) {
            System.out.println(item.getSname());
        }
    }
}

MyBatis工具類：

package cn.sohappy.util;

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.io.InputStream;

public class MyBatisUtil {
    private static InputStream is;
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            is=Resources.getResourceAsStream("mybatis-config.xml");
        } catch (IOException e) {
            e.printStackTrace();
        }
        sqlSessionFactory= new SqlSessionFactoryBuilder().build(is);
    }
    private MyBatisUtil(){}
    public static SqlSession getSession(){
        return sqlSessionFactory.openSession();
    }
}