# mybatis复杂映射


<!--more-->

## 一、一对一
```xml
<mapper namespace="com.example.demo.mapper.OrderMapper">

    <resultMap id="orderMap" type="com.example.demo.pojo.Order">
        <result property="id" column="id"></result>
        <result property="orderTime" column="orderTime"></result>
        <result property="total" column="total"></result>

        <association property="user" javaType="com.example.demo.pojo.User">
            <result property="id" column="uid"></result>
            <result property="username" column="username"></result>
        </association>
    </resultMap>


    <!--resultMap：手动来配置实体属性与表字段的映射关系-->
    <select id="findAll" resultMap="orderMap">
        select *
        from orders o,
             user u
        where o.uid = u.id
    </select>


</mapper>
```

## 二、一对多
```xml
<mapper namespace="com.example.demo.mapper.UserMapper">

    <resultMap id="userMap" type="com.example.demo.pojo.User">
        <result property="id" column="id"></result>
        <result property="username" column="username"></result>
        <result property="password" column="password"></result>
        <result property="birthday" column="birthday"></result>

        <collection property="orderList" ofType="com.example.demo.pojo.Order">
            <result property="id" column="oid"></result>
            <result property="orderTime" column="orderTime"></result>
            <result property="total" column="total"></result>
        </collection>
    </resultMap>


    <!--resultMap：手动来配置实体属性与表字段的映射关系-->
    <select id="findAll" resultMap="userMap">
        select *, o.id oid
        from user u
                 left join orders o on u.id = o.uid
    </select>


</mapper>
```
延迟加载： fetchType="lazy"，assoication、collection可配置该属性,当使用到子属性时才去查询   
也可全局配置：
    ```xml
    <settings>
        <!--开启全局延迟加载功能-->
        <setting name="lazyLoadingEnabled" value="true"/>
    </settings>
    ```

## 三、多对多
同一对多

> 示例代码见：https://gitee.com/ixinglan/mybatis-tec.git