mybatis一对一关联查询

1.

package com.test.entity;

import java.util.Date;

/**
 * 
 * @author Mr
 * 跟数据库表一一对应
 */
public class User {
    
    private int id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
    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 Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public User() {
        super();
        // TODO Auto-generated constructor stub
    }
    public User(String username, Date birthday, String sex,
            String address) {
        super();
        this.username = username;
        this.birthday = birthday;
        this.sex = sex;
        this.address = address;
    }
    public User(int id, String username, Date birthday, String sex,
            String address) {
        super();
        this.id = id;
        this.username = username;
        this.birthday = birthday;
        this.sex = sex;
        this.address = address;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", birthday="
                + birthday + ", sex=" + sex + ", address=" + address + "]";
    }
    
}

2.

package com.test.entity;

import java.util.Date;

/**
 * 订单实体类
 * @author Mr
 * 因为这个类不能完成下面的sql语句的映射，要新建pojo
 */
public class Orders {
    /* SELECT orders.*,userss.username,userss.sex,userss.address FROM orders,userss
     *  WHERE orders.user_id=userss.id*/
    private Integer id;
    private Integer userId;
    private String numbers;
    private Date createtime;
    private String note;
    
    //使用resultMap添加user
    private User user;
    
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    @Override
    public String toString() {
        return "Orders [id=" + id + ", userId=" + userId + ", numbers="
                + numbers + ", createtime=" + createtime + ", note=" + note
                + "]";
    }
    public Orders(Integer id, Integer userId, String numbers, Date createtime,
            String note) {
        super();
        this.id = id;
        this.userId = userId;
        this.numbers = numbers;
        this.createtime = createtime;
        this.note = note;
    }
    public Orders() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public Integer getUserId() {
        return userId;
    }
    public void setUserId(Integer userId) {
        this.userId = userId;
    }
    public String getNumbers() {
        return numbers;
    }
    public void setNumbers(String numbers) {
        this.numbers = numbers;
    }
    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;
    }
}

3.

package com.test.entity;

import java.util.Date;

/**
 * 它的存在是为了解决下面的sql语句的映射
 * SELECT orders.*,userss.username,userss.sex,userss.address 
 * FROM orders,userss WHERE orders.user_id=userss.id
 * 
 * @author Mr
 *
 */
public class OrdersCustom extends Orders{
    //解决这些映射问题
    //userss.username,userss.sex,userss.address
    private String username;
    private String sex;
    private String address;
    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 String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "OrdersCustom [username=" + username + ", sex=" + sex
                + ", address=" + address + "]";
    }
}

4.

<!--  -->
<resultMap type="com.test.entity.Orders" id="OrdersUserResultMap">
    <id column="id" property="id"/>
    <result column="user_id" property="userId"/>
    <result column="numbers" property="numbers"/>
    <result column="createtime" property="createtime"/>
    <result column="note" property="note"/>
        <!-- 配置关联映射
        property 将关联查询的信息映射到每个order的属性
        user到orders:一个用户可以下多个订单：一对多
        orders到user:一个订单只能由一个用户创建：一对一
         -->
        <association property="user" javaType="com.test.entity.User">
            <id column="id" property="id"/>
            <result column="username" property="username"/>
            <result column="sex" property="sex"/>
            <result column="address" property="address"/>
        </association>
</resultMap>
<!-- 引用 resultMap-->
<select id="findOrdersUserResultMap" resultMap="OrdersUserResultMap">
    SELECT orders.*,
    userss.username,
    userss.sex,
    userss.address 
    FROM orders,userss 
    WHERE orders.user_id=userss.id
</select>

5.

package com.test.demo;

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

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.test.dao.OrdersMapperCustom;
import com.test.entity.Orders;

/**
 * 使用resultMap配置关联查询
 * @author Mr
 *
 */
public class Test10 {

    public static void main(String[] args) throws IOException {
        //mybatis核心配置文件
        String resource = "SqlMapConfig.xml";
        //读取配置文件
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //获取工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //获取数据库操作对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        OrdersMapperCustom omc = sqlSession.getMapper(OrdersMapperCustom.class);
        
        List<Orders> list = omc.findOrdersUserResultMap();
        
        for (Orders orders : list) {
            System.out.println(orders.getUser().getUsername());
            System.out.println(orders.getUserId());
        }

    }

}