（五）mybatis之一对一关系

一、需求分析

• 需求：查询订单信息关联查询用户信息
• 分析：一条订单只能由一个消费者来下单，也就是说从订单的角度来说与消费者是一对一的关系。

二、建数据库表和实体对象

• 其中订单表中的字段user_id对应着消费者表的主键user_id，是一对一关系。

Customer.java

package com.shyroke.entity;

public class Customer {
    private int id;
    private String name;
    private String sex;
    private String birthday;

    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 String getSex() {
        return sex;
    }

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

    public String getBirthday() {
        return birthday;
    }

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

    @Override
    public String toString() {
        return "Customer [id=" + id + ", name=" + name + ", sex=" + sex + ", birthday=" + birthday + "]";
    }

}

Order.java

package com.shyroke.entity;

public class Order {
    private int orderId;
    private String Number;
    private String createTime;
    private String note;
    private Customer customer;

    public int getOrderId() {
        return orderId;
    }

    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }

    public String getNumber() {
        return Number;
    }

    public void setNumber(String number) {
        Number = number;
    }

    public String getCreateTime() {
        return createTime;
    }

    public void setCreateTime(String createTime) {
        this.createTime = createTime;
    }

    public String getNote() {
        return note;
    }

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

    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

    @Override
    public String toString() {
        return "Order [orderId=" + orderId + ", Number=" + Number + ", createTime=" + createTime + ", note=" + note
                + ", customer=" + customer + "]";
    }

}

• 在Orders类中创建一个customer属性，将关联查询到的信息映射到Customer的属性中。

三、编写OrderMapper.java接口和OrderMapper.xml配置文件

OrderMappe.java

package com.shyroke.mapper;

import java.util.List;

import com.shyroke.entity.Order;

public interface OrderMapper {
    public List<Order> getOrderCustomList();
}

OrderMappe.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.shyroke.mapper.OrderMapper">
    <resultMap type="com.shyroke.entity.Order" id="orderMap">
        <id column="order_id" property="orderId" />
        <result column="order_number" property="Number" />
        <result column="order_createTime" property="createTime" />
        <result column="order_note" property="note" />

        <association property="customer" javaType="com.shyroke.entity.Customer">
            <id column="user_id" property="id" />
            <result column="user_name" property="name" />
            <result column="user_sex" property="sex" />
            <result column="user_birthday" property="birthday" />
        </association>

    </resultMap>

    <select id="getOrderCustomList" resultMap="orderMap">
         SELECT
            orders.*, customer.user_name, customer.user_sex, customer.user_birthday
        FROM
            orders,
            customer
        WHERE
            orders.user_id = customer.user_id;
    </select>

</mapper>

• association 标签中的property指的是成员变量名，而javaType指的是该成员变量对应的类。

四、注册到总配置文件中

mybatis-config.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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <!-- 配置数据库连接信息 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;useJDBCCompliantTimezoneShift=true&amp;useLegacyDatetimeCode=false&amp;serverTimezone=UTC" />
                <property name="username" value="root" />
                <property name="password" value="" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper class="com.shyroke.mapper.OrderMapper"/>
    </mappers>

</configuration>

五、测试

App.java

package com.shyrolk.firstMybatis;

import java.awt.image.ImageProducer;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import javax.swing.plaf.synth.SynthSeparatorUI;

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.shyroke.entity.Order;
import com.shyroke.mapper.OrderMapper;

/**
 * Hello world!
 *
 */
public class App
{
    public static void main( String[] args ) throws IOException
    {
        String resource="resource/mybatis-config.xml";
        InputStream inputStream=Resources.getResourceAsStream(resource);
        SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(inputStream);

    SqlSession session=sessionFactory.openSession();

    OrderMapper orderMapper=session.getMapper(OrderMapper.class);
    List<Order> orderList=orderMapper.getOrderCustomList();

    System.out.println(orderList);

    }
}

结果：