目录
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;
}