关联查询

现在有两个表，用户表与订单表，其关系如下：

下面用Mybatis实现一对一与一对多查询

一对一：

准备两个表与数据

DROP TABLE IF EXISTS `orders`;
CREATE TABLE `orders` (
                        `id` int(11) NOT NULL AUTO_INCREMENT,
                        `user_id` int(11) NOT NULL COMMENT '下单用户id',
                        `number` varchar(32) NOT NULL COMMENT '订单号',
                        `createtime` datetime NOT NULL COMMENT '创建订单时间',
                        `note` varchar(100) DEFAULT NULL COMMENT '备注',
                        PRIMARY KEY (`id`),
                        KEY `FK_orders_1` (`user_id`),
                        CONSTRAINT `FK_orders_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

INSERT INTO `orders` VALUES ('3', '1', '1000010', '2015-02-04 13:22:35', null);
INSERT INTO `orders` VALUES ('4', '1', '1000011', '2015-02-03 13:22:41', null);
INSERT INTO `orders` VALUES ('5', '10', '1000012', '2015-02-12 16:13:23', null);

CREATE TABLE `user` (
                      `id` int(11) NOT NULL AUTO_INCREMENT,
                      `username` varchar(32) NOT NULL COMMENT '用户名称',
                      `birthday` date DEFAULT NULL COMMENT '生日',
                      `sex` char(1) DEFAULT NULL COMMENT '性别',
                      `address` varchar(256) DEFAULT NULL COMMENT '地址',
                      PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8;

INSERT INTO `user` VALUES ('1', '王五', null, '2', null);
INSERT INTO `user` VALUES ('10', '张三', '2014-07-10', '1', '北京市');
INSERT INTO `user` VALUES ('16', '张小明', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('22', '陈小明', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('24', '张三丰', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('25', '陈小明', null, '1', '河南郑州');
INSERT INTO `user` VALUES ('26', '王五', null, null, null);

实现方法一：使用resultType实现

Orders类

package com.hyx3.one_to_one.pojo;

import javax.jws.soap.SOAPBinding;
import java.util.Date;

public class Orders {

    private Integer id;

    private Integer user_id;

    private String number;

    private Date createtime;

    private String note;

    private User user;

    public User getUser() {
        return user;
    }

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

    public Integer getId() {
        return id;
    }

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

    public Integer getUser_id() {
        return user_id;
    }

    public void setUser_id(Integer user_id) {
        this.user_id = user_id;
    }

    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;
    }

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

User类

package com.hyx3.one_to_one.pojo;

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

public class User {
    private Integer id;
    private String username;// 用户姓名
    private String sex;// 性别
    private Date birthday;// 生日
    private String address;// 地址

    private List<Orders> ordersList;

    public User() {
    }

    public List<Orders> getOrdersList() {
        return ordersList;
    }

    public void setOrdersList(List<Orders> ordersList) {
        this.ordersList = ordersList;
    }



    public User(String username, String sex, Date birthday, String address) {
        this.username = username;
        this.sex = sex;
        this.birthday = birthday;
        this.address = 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 String getSex() {
        return sex;
    }

    public void setSex(String 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 + '\'' +
                ", ordersList=" + ordersList +
                '}';
    }
}

（a）改造POJO：目前已经拥有的实体，没有一个能够映射所有的字段，需要重新创建一个POJO类OrderCustomer，创建一个类，继承字段多的POJO类

package com.hyx3.one_to_one.pojo;

public class OrderCustomer extends Orders {
    private String username;
    private String address;

    public String getUsername() {
        return username;
    }

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

    public String getAddress() {
        return address;
    }

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

    @Override
    public String toString() {
        String string = super.toString();
        return "OrderCustomer{" +
                "username='" + username + '\'' +
                ", address='" + address + '\'' +
                '}'+string;
    }
}

（b）OrdersMapper接口

package com.hyx3.one_to_one.mapper;

import com.hyx3.one_to_one.pojo.OrderCustomer;
import com.hyx3.one_to_one.pojo.Orders;
import com.hyx3.one_to_one.pojo.User;

import java.util.List;

public interface OrderMapper {

    // 1---1
    public List<OrderCustomer> findUserOrders();
}

（c）OrdersMapper.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.hyx3.one_to_one.mapper.OrderMapper">

    <select id="findUserOrders" resultType="ordercustomer">
        select  orders.* ,u.username , u.address from orders,user u where u.id = orders.user_id;
    </select>
</mapper>

（d）测试类

package com.hyx3.one_to_one.test;

import com.hyx3.one_to_one.mapper.OrderMapper;
import com.hyx3.one_to_one.pojo.OrderCustomer;
import com.hyx3.one_to_one.pojo.Orders;
import com.hyx3.one_to_one.pojo.User;
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 org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Demo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream("one_to_one_sqlMapconfig.xml");
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );
    }
    @Test
    public void fun(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List<OrderCustomer> userOrders = mapper.findUserOrders();
        for(OrderCustomer oc : userOrders){
            System.out.println(oc);
        }
    }

}

实现方法一：使用resultMap实现

OrderMapper.class

package com.hyx3.one_to_one.mapper;

import com.hyx3.one_to_one.pojo.OrderCustomer;
import com.hyx3.one_to_one.pojo.Orders;
import com.hyx3.one_to_one.pojo.User;

import java.util.List;

public interface OrderMapper {

    // 1---1
    public List<Orders> findUserOrdersResultMap();


}

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.hyx3.one_to_one.mapper.OrderMapper">

    <resultMap id="orderUserMap" type="orders">
        <id column="id" property="id"></id>
        <result column="user_id" property="user_id"></result>
        <result column="number" property="number"></result>
        <result column="note" property="note"></result>

        <association property="user" javaType="User">
            <id column="user_id" property="id"></id>
            <result column="username" property="username"></result>
            <result column="address" property="address"></result>
        </association>

    </resultMap>

    <select id="findUserOrdersResultMap" resultMap="orderUserMap">
        select  orders.* ,u.username , u.address from orders,user u where u.id = orders.user_id;
    </select>

</mapper>

测试代码

package com.hyx3.one_to_one.test;

import com.hyx3.one_to_one.mapper.OrderMapper;
import com.hyx3.one_to_one.pojo.OrderCustomer;
import com.hyx3.one_to_one.pojo.Orders;
import com.hyx3.one_to_one.pojo.User;
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 org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Demo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream("one_to_one_sqlMapconfig.xml");
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );
    }
  

    @Test
    public void fun1(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List<Orders> userOrders = mapper.findUserOrdersResultMap();
        for(Orders oc : userOrders){
            System.out.println(oc);
        }
    }

 
}

总结：

实现一对一查询

ResultType:

使用resultType比较简单，如果没有对应POJO，就创建一个对应POJO即可。

如果，查询结果没有特殊性的要求，就建议使用ResultType

ResultMap:

需要单独定义ResultMap，实现有些麻烦，

如果对查询的结果有特殊要求（指定结果）使用ResultMap,将关联查询的结果映射到POJO的属性中。

ResultMap可以实现延迟加载，ResultType无法实现延迟加载。

Order对象（顶层）包含User对象（第二层），如果暂未没有用到User属性，就不查询User的信息。

一对多

一对多的关系，只能用ResultMap实现，无法使用resultType实现。

修改POJO，User中添加一个新的属性

Mapper接口：

package com.hyx3.one_to_one.mapper;

import com.hyx3.one_to_one.pojo.OrderCustomer;
import com.hyx3.one_to_one.pojo.Orders;
import com.hyx3.one_to_one.pojo.User;

import java.util.List;

public interface OrderMapper {


    //1-----n
    public List<User> findUserOrder();
}

Mapper.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.hyx3.one_to_one.mapper.OrderMapper">



    <resultMap id="userOrderMap" type="User">
        <id column="id" property="id"></id>
        <result column="username" property="username"></result>
        <result column="birthday" property="birthday"></result>
        <result column="sex" property="sex"></result>
        <result column="address" property="address"></result>

        <collection property="ordersList" javaType="list" ofType="Orders">
            <id column="oid" property="id"></id>
            <result column="createtime" property="createtime"></result>
        </collection>

    </resultMap>

    <select id="findUserOrder" resultMap="userOrderMap">
        select  u.* ,o.id oid, o.createtime from user u left join orders o on u.id = o.user_id;
    </select>
</mapper>

测试类

package com.hyx3.one_to_one.test;

import com.hyx3.one_to_one.mapper.OrderMapper;
import com.hyx3.one_to_one.pojo.OrderCustomer;
import com.hyx3.one_to_one.pojo.Orders;
import com.hyx3.one_to_one.pojo.User;
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 org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Demo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream("one_to_one_sqlMapconfig.xml");
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );
    }


    @Test
    public void fun2(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List<User> userOrder = mapper.findUserOrder222();
        for(User oc : userOrder){
            System.out.println(oc);
        }
    }
}

总结

Mybatis使用resultMap的collection对关联插入的多条记录映射到一个List集合属性中。

如果使用ResultType实现：只能自己手动处理数据，需要使用双层循环遍历，合并记录

ResultMap和ResultType总结

ResultType:

作用：

将查询结果按照SQL列名和POJO属性名一致，进行映射

场景：

常见的一些明细记录，比如：用户购买商品明细，将关联查询全部信息都要展示在页面上，此时可以直接使用ResultType，将一条记录映射到POJO中。前端页面变量List<POJO>

数据只有一层的情况。

ResultMap:

使用collection和association完成一对多和一对一高级映射（对结果又特殊的映射要求）

Association：

作用:：将关联查询的信息映射到一个POJO对象中

场景：一对一，查询订单以及关联用户

Collection：

作用：将关系查询的信息映射到一个集合List中。

场景：一对多，查询用户以及关联订单

多对多

多对多的关系，需要借助第三表来存储这个关系，无论是添加、还是删除、查询，本质都是对第三张表进行的操作。

商品和订单的关系

用户和角色的关系

用户和权限的关系

Mybatis使用关联查询

关联查询

一对一：

准备两个表与数据

实现方法一：使用resultType实现

Orders类

User类

（a）改造POJO：目前已经拥有的实体，没有一个能够映射所有的字段，需要重新创建一个POJO类OrderCustomer，创建一个类，继承字段多的POJO类

（b）OrdersMapper接口

（c）OrdersMapper.xml

（d）测试类

实现方法一：使用resultMap实现

OrderMapper.class

OrderMapper.xml

测试代码

总结：

实现一对一查询

ResultType:

ResultMap:

一对多

修改POJO，User中添加一个新的属性

Mapper接口：

Mapper.xml

测试类

总结

ResultMap和ResultType总结

ResultType:

ResultMap:

Association：

Collection：

多对多

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