条件构造器

目录

命名DAO对象

​编辑

组装查询条件

组装查询包含条件  

组装排序条件  

 组装删除条件

 条件的优先级

实现子查询  

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命名DAO对象

组装查询条件

代码如下 

 @RequestMapping("/test02")
    public List<User> Test02(){
       //创建条件构造器对象
       QueryWrapper<User> userQueryWrapper = new QueryWrapper<User>();
       //select * from t_user where user_name='admin'
       userQueryWrapper.eq("user_name","admin");
       //select * from t_user where user_name='admin' and money between  1300 and 1500
       userQueryWrapper.between("money",1300,1500);
       List<User> list = dao.selectList(userQueryWrapper);
       return list;
   }

组装查询包含条件  

 

@RequestMapping("/test03")
    public List<User> Test03(){
       //查询用户名包含a，年龄在20到30之间，并且邮箱不为null的用户信息
       QueryWrapper<User> userQueryWrapper = new QueryWrapper<User>();
       userQueryWrapper.like("user_name","a").between("money",500,800).isNotNull("id");
       List<User> list = dao.selectList(userQueryWrapper);
       return list;
   }

组装排序条件  

 

@RequestMapping("/test04")
    public List<User> Test04(){
       //按money升序asc排列,如果money相同就按id排列
       QueryWrapper<User> userQueryWrapper = new QueryWrapper<User>();
       userQueryWrapper.orderByAsc("money").orderByDesc("id");
       List<User> list = dao.selectList(userQueryWrapper);
       return list;
   }

 组装删除条件

 @RequestMapping("/test05")
    public int  Tsst05(){
       // //删除money为空的用户

       QueryWrapper<User> userQueryWrapper = new QueryWrapper<User>();
        userQueryWrapper.isNull("money");
       int count = dao.delete(userQueryWrapper);
       return count;
   }

 条件的优先级

@RequestMapping("/test07")
    public List<User> Test07(){
       //将money大于1000并且用户名是admin的
       QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
       userQueryWrapper.like("user_name","admin").gt("money",1000);
       List<User> list = dao.selectList(userQueryWrapper);
       return list;

   }

实现子查询  

@RequestMapping("/test06")
    public List<User> Test06(){
       QueryWrapper<User> userQueryWrapper = new QueryWrapper<>();
       userQueryWrapper.inSql("id","select id from t_user where id<=3");
       List<User> list = dao.selectList(userQueryWrapper);
       return list;
   }