Mybatis关联查询之三

MyBatis的关联查询之自关联

自关联

一、entity实体类

public class City {
    private Integer cid;
    private String cname;
    private Integer pid;

    //自关联集合   代表的是当前City对象的自己集合
    public List<City> childCitys;

    public Integer getCid() {
        return cid;
    }

    public void setCid(Integer cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public Integer getPid() {
        return pid;
    }

    public void setPid(Integer pid) {
        this.pid = pid;
    }

    public List<City> getChildCitys() {
        return childCitys;
    }

    public void setChildCitys(List<City> childCitys) {
        this.childCitys = childCitys;
    }

    @Override
    public String toString() {
        return "City{" +
                "cid=" + cid +
                ", cname='" + cname + '\'' +
                ", pid=" + pid +
                ", childCitys=" + childCitys +
                '}';
    }
}

二、dao层

//自关联  查询河南省下所有子集
    public City getCityAndChild(Integer cid);

三、dao.xml 小配置

<!--自关联-->
    <resultMap id="CityAndChildCity" type="com.marketsys.entity.City">
        <id column="cid" property="cid"></id>
        <result column="cname" property="cname"></result>
        <result column="pid" property="pid"></result>
        <collection property="childCitys" ofType="com.marketsys.entity.City" select="getCity" column="cid">
            <id column="cid" property="cid"></id>
            <result column="cname" property="cname"></result>
            <result column="pid" property="pid"></result>
        </collection>
    </resultMap>
    <select id="getCityAndChild" resultMap="CityAndChildCity">
        select * from city where cid=#{cid}
    </select>
    <select id="getCity" resultMap="CityAndChildCity">
        select * from city where pid=#{cid}
    </select>

四、test测试类

SqlSession sqlSession= MybatisUtil.getSqlSession();
    URoleTestDao mapper=sqlSession.getMapper(URoleTestDao.class);

//自关联
    @Test
    public void test4(){
        City city = mapper.getCityAndChild(410000);
        System.out.println(city.toString());
    }