MyBatis多表操作-----多对多操作

多对多操作较之前没有太大的变化，搭配好环境之后进行查询

与之前相比在Mapper层内容有一些增加

由于是多对多的关系，相对于每一个表中的数据都是一对多的关系，那么在增加字段时需要使用@Many

 @Result(property = "teas",column = "sid",javaType = List.class, many = @Many(select = "com.ryh.test.mapper.TeaMapper.selectTeasBySid")) 

讯享网
MyBatis自带的功能无法查询List<>中的数据，于是需要在其中增加功能

首先对TeaMapper进行操作

将如上功能模块复制后进行修改，在里面添加SQL语句

讯享网"SELECT * ", "FROM tea ", "WHERE tid in ", "(SELECT tid ", "FROM teastu ", "WHERE sid= #{sid,jdbcType=INTEGER}) " 

意为在另一个表中查找tid属性值，其中tid来自于teastu表中，sid=tid的值

在下面将方法名重新命名以免重复

 @Select({ 
    "SELECT * ", "FROM tea ", "WHERE tid in ", "(SELECT tid ", "FROM teastu ", "WHERE sid= #{sid,jdbcType=INTEGER}) " }) @Results({ 
    @Result(column="tid", property="tid", jdbcType=JdbcType.INTEGER, id=true), @Result(column="tname", property="tname", jdbcType=JdbcType.VARCHAR) }) List<Tea> selectTeasBySid(Integer sid); 

类比于TeaMapper，对StuMapper也进行修改

关于多对多如何进行删除操作：
在TeaStuMapper中添加部分删除的操作

在其中添加了只删除tid和只删除sid的功能

讯享网@Delete({ 
    "delete from teastu", "where tid = #{tid,jdbcType=INTEGER}" }) int deleteByTid(Integer tid); @Delete({ 
    "delete from teastu", "where sid = #{sid,jdbcType=INTEGER}" }) int deleteBySid(Integer sid); 

注意：在增加数据的时候，由于多对多关系中有一个中间表，所以也需要新建中间表将数据间的关系用对象传入操作中

public class TeaService { 
    private SqlSessionFactory ssf; public TeaService() { 
    InputStream is=this.getClass().getClassLoader().getResourceAsStream("mybatis.cfg.xml"); ssf=new SqlSessionFactoryBuilder().build(is); } @Test public void deleteTea(){ 
    SqlSession session=ssf.openSession(); try { 
    int tid=98; session.delete("com.ryh.test.mapper.TeaStuMapper.deleteByTid",tid); session.delete("com.ryh.test.mapper.TeaMapper.deleteByPrimaryKey",tid); session.commit(); }catch (Exception e){ 
    session.rollback(); e.printStackTrace(); } session.close(); } @Test public void add(){ 
    SqlSession session=ssf.openSession(); try{ 
    Tea tea1=new Tea(); tea1.setTid(98); tea1.setTname("鲁迅"); Tea tea2=new Tea(); tea2.setTid(99); tea2.setTname("胡适"); Stu stu1=new Stu(); stu1.setSid(88); stu1.setSname("林徽因"); Stu stu2=new Stu(); stu2.setSid(89); stu2.setSname("徐志摩"); session.insert("com.ryh.test.mapper.TeaMapper.insert",tea1); session.insert("com.ryh.test.mapper.TeaMapper.insert",tea2); session.insert("com.ryh.test.mapper.StuMapper.insert",stu1); session.insert("com.ryh.test.mapper.StuMapper.insert",stu2); TeaStuKey st1=new TeaStuKey(); st1.setTid(98); st1.setSid(88); TeaStuKey st2=new TeaStuKey(); st2.setTid(98); st2.setSid(89); TeaStuKey st3=new TeaStuKey(); st3.setTid(99); st3.setSid(88); TeaStuKey st4=new TeaStuKey(); st4.setTid(99); st4.setSid(89); session.insert("com.ryh.test.mapper.TeaStuMapper.insert",st1); session.insert("com.ryh.test.mapper.TeaStuMapper.insert",st2); session.insert("com.ryh.test.mapper.TeaStuMapper.insert",st3); session.insert("com.ryh.test.mapper.TeaStuMapper.insert",st4); session.commit(); }catch (Exception e){ 
    session.rollback(); e.printStackTrace(); } session.close(); } @Test public void queryTeas(){ 
    SqlSession session = ssf.openSession(); TeaExample example = new TeaExample(); List<Tea> list=session.selectList("com.ryh.test.mapper.TeaMapper.selectByExample",example); list.forEach(t-> { 
    List<Stu> stus = t.getStus(); System.out.println(t.getTname()); stus.forEach(s-> System.out.print(s.getSname()+",")); System.out.println(); }); session.close(); } @Test public void queryStus(){ 
    SqlSession session = ssf.openSession(); StuExample example = new StuExample(); List<Stu> list=session.selectList("com.ryh.test.mapper.StuMapper.selectByExample",example); list.forEach(s-> { 
    List<Tea> teas = s.getTeas(); System.out.println(s.getSname()); teas.forEach(t-> System.out.print(t.getTname()+",")); System.out.println(); }); session.close(); } }