1、数据库表

CREATE TABLE `country` (  `cid` int(4) NOT NULL AUTO_INCREMENT COMMENT '国家id',  `cname` varchar(20) COLLATE utf8_unicode_ci NOT NULL,  PRIMARY KEY (`cid`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci；CREATE TABLE `provincial` (  `pid` int(4) NOT NULL AUTO_INCREMENT,  `pname` varchar(20) COLLATE utf8_unicode_ci NOT NULL,  `countryid` int(4) NOT NULL,  PRIMARY KEY (`pid`)) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci；

2、实体类

package cn.bdqn.bean;/** *国家的实体类 */public class Country {    private Integer cId; // 国家的编号    private String cName; // 国家的名称    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 Country(Integer cId, String cName) {        super();        this.cId = cId;        this.cName = cName;    }    public Country() {        super();    }    @Override    public String toString() {        return "Country [cId=" + cId + ", cName=" + cName;    }}

package cn.bdqn.bean;/** *  *省会对应的实体类 */public class Provincial {    private Integer pId; // 省会的编号    private String pName; // 省会名称    // 关联的国家属性    private Country country;    public Country getCountry() {        return country;    }    public void setCountry(Country country) {        this.country = country;    }    public Integer getpId() {        return pId;    }    public void setpId(Integer pId) {        this.pId = pId;    }    public String getpName() {        return pName;    }    public void setpName(String pName) {        this.pName = pName;    }    public Provincial(Integer pId, String pName) {        super();        this.pId = pId;        this.pName = pName;    }    public Provincial() {        super();    }    /*@Override    public String toString() {        return "Provincial [pId=" + pId + ", pName=" + pName + ", country="                + country + "]";    }*/}

3、mybatis.xml配置文件

4、Dao层接口

package cn.bdqn.dao;import cn.bdqn.bean.Provincial;public interface ProvincialDao {    /**     * 根据省会的id查询出省会和对应国家的信息       */    Provincial selectProvincialById(Integer pId);}

5、Mapper.xml

     
         
              select cid,cname from country         where cid = #{countryid}        
             
              
              
              
          
            
             select pid,pname,countryid from provincial       where pid = #{pid}    
     

6、测试类

package cn.bdqn.test;import org.apache.ibatis.session.SqlSession;import org.apache.log4j.Logger;import org.junit.After;import org.junit.Before;import org.junit.Test;import cn.bdqn.bean.Provincial;import cn.bdqn.dao.ProvincialDao;import cn.bdqn.util.MybatisUtil;public class Test1 {    private Logger logger = Logger.getLogger(Test1.class);    SqlSession session;    ProvincialDao dao;    @Before    public void before() {        // 因为需要关闭session 需要把session提取出去        session = MybatisUtil.getSqlSession();        dao = session.getMapper(ProvincialDao.class);    }    @After    public void after() {        if (session != null) {            session.close();        }    }    @Test    public void test1() {        Provincial provincial = dao.selectProvincialById(1);        /*logger.debug("provincialId=1======>provincial:" + provincial);*/        /*logger.debug("provincialId=1======>country:" + provincial.getCountry());*/    }}