mybatis-一对一，一对多查询

1.一对一查询：
根据角色来查询所对应的people，这里是通过age来关联两个表的。
需求：根据role 的age_id来查询对应的people
实现：因为它们关联的字段是age，在xml文件做一对一映射使用association映射age所对应的实体类即可。
role pojo：

package com.shuai.pojo;

import lombok.Data;

@Data
public class Role {
    private String workNmame;
    private People people;
}

mapper xml文件：

<?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.shuai.mapper.PeopleMapper">
    <resultMap id="RoleMapper" type="com.shuai.pojo.Role">
        <result property="workNmame" column="work_name"></result>
        <association property="people" javaType="com.shuai.pojo.People">
            <result property="name" column="name"></result>
            <result property="age" column="age"></result>
        </association>
    </resultMap>
    <select id="findById" resultMap="RoleMapper" parameterType="int" >
    select * from people,role where people.age=role.age_id and age_id=#{id};
    </select>
</mapper>

2.一对多查询：一对多基于一对一的基础上的，只是对于age的映射改成关于实体类的集合，association改为collection做相关映射。
role

package com.shuai.pojo;

import lombok.Data;

import java.util.List;

@Data
public class Role {
    private String workNmame;
    private List<People> people;
}

mapper xml

<?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.shuai.mapper.PeopleMapper">
    <resultMap id="RoleMapper" type="com.shuai.pojo.Role">
        <result property="workNmame" column="work_name"></result>
        <collection property="people" ofType="com.shuai.pojo.People">
            <result property="name" column="name"></result>
            <result property="age" column="age"></result>
        </collection>
    </resultMap>
    <select id="findById" resultMap="RoleMapper" parameterType="int" >
    select * from people,role where people.age=role.age_id and age_id=#{id};
    </select>
</mapper>