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05-mybatis的多表操作-一对多配置实现

发布时间：2025-02-02 10:13:58编辑：雪饮阅读（）

在上篇中的User.java中新增orderList属性并生成getter与setter以及重新生成toString
package sp28.domain;

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

public class User {

    private int id;
    private String username;
    private String password;
    private Date birthday;
    private List<Order> orderList;

    public List<Order> getOrderList() {
        return orderList;
    }

    public void setOrderList(List<Order> orderList) {
        this.orderList = orderList;
    }

    public Date getBirthday() {
        return birthday;
    }

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



    public int getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", birthday=" + birthday +
                ", orderList=" + orderList +
                '}';
    }

}
然后在UserMapper.java中新增findAll用来查询所有（包含每个用户的订单列表）
package sp28.dao;

import sp28.domain.User;

import java.util.List;

public interface UserMapper {
    public List<User> findAll();
}
然后在UserMapper.xml中去实现findAll及结果集映射
<?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="sp28.dao.UserMapper">
    <resultMap id="userMap" type="user">
        <!--
        column：数据表的字段名称
        property:实体的属性名称
        -->
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="password" column="password"/>
        <result property="birthday" column="birthday"/>
        <!--
        配置集合信息
        property：集合名称
        ofType: 集合中元素的数据类型
        -->
        <collection property="orderList" ofType="order">
            <!--封装order的数据-->
            <id property="id" column="oid"/>
            <result column="ordertime" property="ordertime"/>
            <result column="total" property="total"/>
        </collection>
    </resultMap>
    <select id="findAll" resultMap="userMap">
        select *,o.id oid from user u,orders o where u.id=o.uid
    </select>
</mapper>
然后新增测试方法来测试
@Test
public void test2() throws IOException {
    InputStream resourceAsStream= Resources.getResourceAsStream("sqlMapConfig.xml");
    SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);
    SqlSession sqlSession=sqlSessionFactory.openSession();
    UserMapper mapper=sqlSession.getMapper(UserMapper.class);
    List<User> userList=mapper.findAll();
    for (User user : userList) {
        System.out.println(user);
    }
    sqlSession.close();
}
这里实际上select *,o.id oid from user u,orders o where u.id=o.uid查询出来user的记录会重复。
在数据库中观感不是很好，但用上面的结果集映射后，就能形成不重复的user记录为主导，每个user的orderList来归档属于自己的order。
而且这样有个弊端就是，只能查询到包含有订单的用户。