MyBatis 对象中含有对象的查询

//类
public class Oldman {

    private int id;
    private String name;
    private String sex;
    //private int age;
    private String st;
    private String hj;//户籍
    private String sfz;//身份证 //AA BB CC DDDD EE FF HH I J
    private String csny;//出生年月
    private String jjlxr;//紧急联系人
    private String  phone;//电话
    private String  adress;//地址
    private Bed bed;//床位
　 private Hugong hg;//护工

｝

　　

Mapper.XML中

    
//做好映射
    <resultMap id="OldmanResult" type="com.shiro.YangLaoYuan.entity.Oldman">
        <id property="id" column="oldman_id" />
        <result property="name" column="name"/>
        <result property="sex" column="sex"/>
        <result property="sfz" column="sfz"/>
        <result property="st" column="st"/>
        <result property="hj" column="hj"/>
        <result property="jjlxr" column="jjlxr"/>
        <result property="phone" column="phone"/>
        <result property="adress" column="adress"/>
        <result property="rz" column="rz"/>
        <result property="cy" column="cy"/>
        <result property="desc" column="desc"/>
//该标签      
  <association property="hg" column="oldman_hg_id" javaType="com.shiro.YangLaoYuan.entity.Hugong" resultMap="HugongResult"/>
        <association property="bed" column="oldman_bed_id" javaType="com.shiro.YangLaoYuan.entity.Bed" resultMap="BedResult"/>

    </resultMap>
//护工类型
    <resultMap id="HugongResult" type="com.shiro.YangLaoYuan.entity.Hugong">
        <id property="id" column="hugong_id"/>
        <result property="name" column="hugong_name"/>

    </resultMap>
//床位类型
    <resultMap id="BedResult" type="com.shiro.YangLaoYuan.entity.Bed">
        <id property="id" column="bed_id"/>
        <result property="info" column="bed_info"/>
    </resultMap>

//select语句
<select id="findOldmans"  resultMap="OldmanResult">
   SELECT
	a.id AS oldman_id,
	a.name,
	a.sex,
	a.sfz,
	a.st,
	a.hj,
	a.jjlxr,
	a.phone,
	a.adress,
	b.id AS bed_id,
	a.bed AS oldman_bed_id,
	b.info AS bed_info,
	a.hg AS oldman_hg_id,
	c.id AS hugong_id,
	c.name AS hugong_name,
	a.rz,
	a.cy,
	a.DESC
FROM
	sys_oldman a
	LEFT JOIN sys_bed b ON a.bed = b.id
	LEFT JOIN sys_hugong c ON a.hg = c.id
</select>

　总结：　

Get 和set以及toString方法已经省略，不要忘记，没有get和set方法时会报错滴。 

 

//主键
<id property="id" column="oldman_id" />

//result 代表返回的一般结果的映射 column是数据库返回的列名 property则是我们类中的定义名 
<result property="name" column="name"/>   

//association 是一对一 或 多对一 咱们的一个老人对应一个床位和一个护工，所以使用一对一的方式 如果要通过本对象的1来获取多可以使用collection
<association property="hg" column="oldman_hg_id" javaType="com.shiro.YangLaoYuan.entity.Hugong" resultMap="HugongResult"/> 

如果要深入理解association/collection可参阅https://blog.51cto.com/yuqian2203/2130538