MyBatis之手動映射之一對一關係

案例背景:

數據庫表中一個訂單對應着一個用戶信息

根據一個訂單ID只可以查詢出一條用戶記錄

我們需要查詢出所有的訂單信息並且信息中包含有對應的用戶記錄

補充:

同以往Order的定義不同,Order中需要封裝User屬性

一.案例展示

1.測試準備

①數據庫mysql一枚

②database名爲batistest且表名爲user和order

③項目工程

2.代碼展示(着重關注OrderMapper.xml的配置)

***pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.howie</groupId>
    <artifactId>mybatis_manual_mapping_one2one</artifactId>
    <version>1.0-SNAPSHOT</version>
    
    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <!--單元測試-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!--mysql驅動-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <!--log4j-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>
</project>

***bean.properties

OrderService=com.howie.service.impl.OrderServiceImpl

***db.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/batistest?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

***log4j.properties

#log4j日誌級別如下：
#A：off     最高等級，用於關閉所有日誌記錄。
#B：fatal   指出每個嚴重的錯誤事件將會導致應用程序的退出。
#C：error   指出雖然發生錯誤事件，但仍然不影響系統的繼續運行。
#D：warn    表明會出現潛在的錯誤情形。
#E：info    一般和在粗粒度級別上，強調應用程序的運行全程。
#F：debug   一般用於細粒度級別上，對調試應用程序非常有幫助。
#G：all     最低等級，用於打開所有日誌記錄。
#但log4j只建議使用4個級別，優先級從高到低分別是:
#error>warn>info>debug
log4j.rootLogger=debug,systemOut,logFile
#輸出到控制檯
log4j.appender.systemOut=org.apache.log4j.ConsoleAppender
log4j.appender.systemOut.layout=org.apache.log4j.PatternLayout
log4j.appender.systemOut.layout.ConversionPattern=[%-5p][%-22d{yyyy/MM/dd HH:mm:ssS}][%l]%n%m%n
log4j.appender.systemOut.Target=System.out
#輸出到文件
log4j.appender.logFile=org.apache.log4j.FileAppender
log4j.appender.logFile.layout=org.apache.log4j.PatternLayout
log4j.appender.logFile.layout.ConversionPattern=[%-5p][%-22d{yyyy/MM/dd HH:mm:ssS}][%l]%n%m%n
log4j.appender.logFile.File=E:/log/log4j.log
log4j.appender.logFile.Encoding=UTF-8
#將日誌輸記錄到MySQL數據庫
#log4j.appender.logDB = org.apache.log4j.jdbc.JDBCAppender
#log4j.appender.logDB.layout = org.apache.log4j.PatternLayout
#log4j.appender.logDB.Driver = com.mysql.jdbc.Driver
#log4j.appender.logDB.URL = jdbc:mysql://localhost:3306/log4j?characterEncoding=utf-8
#log4j.appender.logDB.User = root
#log4j.appender.logDB.Password = root
#log4j.appender.logDB.Sql = INSERT INTO t_log4j(project_name,create_date,level,category,file_name,thread_name,line,all_category,message)values('mybatis','%d{yyyy-MM-ddHH:mm:ss}','%p','%c','%F','%t','%L','%l','%m')
#若出現問題：Log4j: ERROR Failed to load driver, java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
#解決方法：將log4j.properties 中每行後面的空格都刪除就解決了.

***SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <!--
        從外部文件db.properties讀取數據庫連接信息
    -->
    <properties resource="db.properties"/>

    <!--配置log4j日誌-->
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <!--批量起別名-->
    <typeAliases>
        <package name="com.howie.pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--獲取db文件中的數據-->
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <!--批量掃描mapper-->
    <mappers>
        <!--<mapper resource="XxxMapper.xml"/>-->
        <package name="com.howie.mapper"/>
    </mappers>
</configuration>

***BeanFactory.java

package com.howie.utils;


import org.apache.ibatis.session.SqlSession;

import java.lang.reflect.Constructor;
import java.util.ResourceBundle;

/**
 *  Bean工廠對象
 *  方法:
 *    傳遞接口,傳遞的是接口的class文件對象
 *    返回實現類的對象
 *
 *    泛型: 本身沒有類型,未知的數據類型
 *    調用的時候,傳遞什麼,就是什麼類型
 */
public class BeanFactory {
    public static <T>T newInstance(Class<T> clazz){
        //獲取傳遞的接口名
        String name = clazz.getSimpleName();
        //讀取配置文件
        ResourceBundle resourceBundle = ResourceBundle.getBundle("bean");
        String className = resourceBundle.getString(name);
        //反射創建對象
        try {
            return (T)Class.forName(className).newInstance();
        }catch (Exception ex){
            ex.printStackTrace();
        }
        return null;
    }

    /**
     *  帶參構造
     * @param clazz
     * @param sqlSession
     * @param <T>
     * @return
     */
    public static <T>T newInstance(Class<T> clazz, SqlSession sqlSession){
        //獲取傳遞的接口名
        String name = clazz.getSimpleName();
        //讀取配置文件
        ResourceBundle resourceBundle = ResourceBundle.getBundle("bean");
        String className = resourceBundle.getString(name);
        //獲取帶參構造函數
        try {
            Constructor constructor = Class.forName(className).getConstructor(SqlSession.class);
            Object[] params = {sqlSession};
            //反射創建對象
            return (T)constructor.newInstance(params);
        }catch (Exception ex){
            ex.printStackTrace();
        }
        return null;
    }
}

***Order.java

package com.howie.pojo;

import java.util.Date;

/**
 * @Author weihuanwen
 * @Date 2019/8/12 11:23
 * @Version 1.0
 */
public class Order {
    private int id;
    private int userId;
    private String number;
    private Date createtime;
    private String note;
    private User user;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "Order{" +
                "id=" + id +
                ", userId=" + userId +
                ", number='" + number + '\'' +
                ", createtime=" + createtime +
                ", note='" + note + '\'' +
                ", user=" + user +
                '}';
    }
}

***User.java

package com.howie.pojo;

import com.sun.org.apache.xpath.internal.operations.Or;

import java.util.Date;
import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/9 9:54
 * @Version 1.0
 */
public class User {

    private Integer id;
    private String username;
    private Integer sex;
    private Date birthday;
    private String address;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getSex() {
        return sex;
    }

    public void setSex(Integer sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", sex=" + sex +
                ", birthday=" + birthday +
                ", address='" + address + '\'' +
                '}';
    }
}

***OrderMapper.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.howie.mapper.OrderMapper">
    <!--是否開啓二級緩存(開啓,則打開註釋)-->
    <!--<cache/>-->

    <!--查詢所有訂單-->
    <select id="queryOrders" resultMap="orderResultMap">
        SELECT
            o.`id`,
            o.`user_id` userId,
            o.`number`,
            o.`createtime`,
            o.`note`,
            u.`id` uid,
            u.`username`,
            u.`address`
        FROM
            `order` o
            LEFT JOIN `user` u ON o.`user_id` = u.`id`
    </select>
    <!--手動映射-->
    <resultMap id="orderResultMap" type="Order">
        <!--基本屬性封裝-->
        <id column="id" property="id"/>
        <id column="userId" property="userId"/>
        <id column="number" property="number"/>
        <id column="createtime" property="createtime"/>
        <id column="note" property="note"/>
        <!--完成一對一中user屬性封裝-->
        <association property="user" javaType="user">
            <id column="uid" property="id"/>
            <result column="username" property="username"/>
            <result column="address" property="address"/>
        </association>
    </resultMap>
</mapper>

***OrderMapper.java

package com.howie.mapper;

import com.howie.pojo.Order;

import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/12 11:24
 * @Version 1.0
 */
public interface OrderMapper {

    /**
     * 查詢所有的訂單
     * @return
     */
    List<Order> queryOrders();
}

***OrderService.java

package com.howie.service;

import com.howie.pojo.Order;

import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/12 11:34
 * @Version 1.0
 */
public interface OrderService {

    /**
     * 查詢所有的訂單
     * @return
     */
    List<Order> queryOrders();
}

***OrderServiceImpl.java

package com.howie.service.impl;

import com.howie.mapper.OrderMapper;
import com.howie.pojo.Order;
import com.howie.service.OrderService;
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;
import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/12 11:35
 * @Version 1.0
 */
public class OrderServiceImpl implements OrderService {

    private static SqlSession sqlSession;
    private static OrderMapper orderMapperImpl;

    static {
        try {
            SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();
            //加載SqlMapConfig.xml文件
            InputStream is = Resources.getResourceAsStream("SqlMapConfig.xml");
            SqlSessionFactory ssf = ssfb.build(is);
            sqlSession = ssf.openSession();
            orderMapperImpl = sqlSession.getMapper(OrderMapper.class);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 查詢所有的訂單信息
     * @return
     */
    @Override
    public List<Order> queryOrders() {
        return orderMapperImpl.queryOrders();
    }
}

***OrderController.java

package com.howie.controller;

import com.howie.pojo.Order;
import com.howie.service.OrderService;
import com.howie.utils.BeanFactory;
import org.junit.Test;

import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/12 11:41
 * @Version 1.0
 */
public class OrderController {

    private OrderService orderService = BeanFactory.newInstance(OrderService.class);

    @Test
    public void queryOrders(){
        List<Order> orders = orderService.queryOrders();
        orders.forEach(System.out::println);
    }
}

3.測試

執行queryOrders()後控制檯輸出

Order{id=1, userId=3, number='1000010', createtime=Wed Feb 04 13:22:35 CST 2015, note='質量很好', user=User{id=3, username='王五', sex=null, birthday=null, address='廣州'}}
Order{id=2, userId=3, number='1000011', createtime=Tue Feb 03 13:22:41 CST 2015, note='非常漂亮', user=User{id=3, username='王五', sex=null, birthday=null, address='廣州'}}
Order{id=3, userId=4, number='1000012', createtime=Thu Feb 12 16:13:23 CST 2015, note='物超所值', user=User{id=4, username='趙六', sex=null, birthday=null, address='深圳'}}