Mybatis一对一映射

查询某个订单的订单内容和用户信息

实现一个订单类的子类 添加订单表中没有的User属性

实现子类 继承订单类

package edu.ccit.cn.domain;

/**
 * @program: Mybatis03_tables
 * @description
 * @author: LIANG
 * @create: 2021-06-01 15:34
 **/
public class OrdersExpand 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() {
        return "OrdersExpand{" +
                "username='" + username + '\'' +
                ", address='" + address + '\'' +
                '}'+super.toString();
    }
}

<select id="findOrdersById" parameterType="int" resultType="edu.ccit.cn.domain.OrdersExpand">
        SELECT
            o.*,u.username,u.address
        FROM
            orders o,user u
        where
            o.user_id=u.id
            and o.id=#{id}
    </select>

直接在订单类中添加User属性

sql片段

<sql id="select_orders">
        orders .*
    </sql>
    <sql id="select_user">
        user.username,user.address
    </sql>

定义resultMap
assocation用于嵌套对象 column为列明 property为属性名

<resultMap id="Orders_user" type="Orders">
   <result column="id" property="id"></result>
   <result column="number" property="number"></result>
   <result column="createtime" property="createtime"></result>
   <!--关联内部对象-->
   <association property="user" javaType="User">
       <result column="username" property="username"></result>
       <result column="address" property="address"></result>
   </association>
</resultMap>

<select id="findOrdersById02" parameterType="int" resultMap="Orders_user">
        select
        <include refid="select_orders"></include>,
        <include refid="select_user"></include>
        from
            orders,user
        where
            orders.user_id=user.id and orders.id=3
    </select>