Mybatis resultMap标签继承、复用、嵌套方式

create table `score` (

    `id` int comment '主键' ,

    `math` float comment '数学成绩' ,

    `history` float comment '历史成绩' ,

    primary key (`id`)

)

create table `member` (

    `id` int comment '主键' ,

    ` name ` varchar comment '姓名' ,

    `group_id` int comment '所属组group表id' ,

    `score_id` int comment '成绩Score表id' ,

    primary key (`id`)

)

create table ` group ` (

    `id` int comment '主键' ,

    ` name ` varchar comment '组名' ,

    primary key (`id`)

)

/** 成绩类 */

public class Score {

    private Integer id;

    /** 数学成绩 */

    private Float math;

    /** 历史成绩 */

    private Float hitory;

    ...getter And setter...

}

/** 成员类 */

public class Member {

    private Integer id;

    /** 姓名 */

    private String name;

    /** 分数对象 */

    private Score score;

    ...getter And setter...

}

/** 组类 */

public class Group {

    private Integer id;

    /** 组名 */

    private String groupName;

    /** 成员 */

    private List<Member> members;

    ...getter And setter...

}

<? 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.example.BeanMapper" >

    <!-- Score实体类映射 -->

    < resultMap id = "scoreMap" type = "com.example.Score" >

        < id column = "id" jdbcType = "INTEGER" property = "id" />

        < result column = "math" jdbcType = "FLOAT" property = "math" />

        < result column = "history" jdbcType = "FLOAT" property = "history" />

    </ resultMap >

    <!-- Member实体类映射 -->

    < resultMap id = "memberMap" type = "com.example.Member" >

        < id column = "id" jdbcType = "INTEGER" property = "id" />

        < result column = "name" jdbcType = "VARCHAR" property = "name" />

    </ resultMap >

    <!-- Group实体类映射 -->

    < resultMap id = "groupMap" type = "com.example.Group" >

        < id column = "id" jdbcType = "INTEGER" property = "id" />

        < result column = "name" jdbcType = "VARCHAR" property = "groupName" />

    </ resultMap >

</ mapper >

<? 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.example.DemoMapper" >

    <!-- extends: 继承 -->

    < resultMap id = "fullMemberMap" extends = "com.example.BeanMapper.memberMap" type = "com.example.Member" >

        <!-- association: 复用已存在的resultMap，单JavaBean属性时使用

                        使用javaType属性指定JavaBean的类型

                        跨文件引用需指定namespace -->

        <!-- columnPrefix: 只从 score_ 开头的字段为当前resultMap取值 -->

        < association   property = "score" resultMap = "com.example.BeanMapper.scoreMap" javaType = "com.example.Score" columnPrefix = "score_" />

    </ resultMap >

    < resultMap id = "fullGroupMap" extends = "com.example.BeanMapper.groupMap" type = "com.example.Group" >

        <!-- collection: 复用已存在的resultMap，JavaBean集合属性时使用

                        使用ofType属性指定JavaBean的类型

                        同文件引用无需指定namespace -->

        <!-- columnPrefix: 只从 member_ 开头的字段为当前resultMap取值

                        进入fullMemberMap内嵌套的scoreMap时前缀 member_ 会被去除，即 member_score_id 字段才能被scoreMap正确接收 -->

        < collection property = "members" ofType = "com.example.Member" resultMap = "fullMemberMap" columnPrefix = "member_" />

    </ resultMap >

    <!-- 直接引用最终的resultMap，并根据columnPrefix属性设置的前缀为各个字段指定不同的别名 -->

    < select id = "selectGroupById" parameterType = "java.lang.Integer" resultMap = "fullGroupMap" >

        select g.id, g.name,

                m.id member_id, m.name member_name,

                s.id member_score_id, s.math member_score_math, s.history member_score_history

          from `group` g

            left join `member` m on m.group_id = g.id

            left join `score` s on s.id = m.score_id

          where g.id = #{id,jdbcType=INTEGER}

    </ select >

</ mapper >