anchor.diff:    var pool=new ConnectionPool(host:'localhost',port:3306,user:'root',db:'vocabulary',max:5);
     var query=await pool.prepare('insert into userinfo(Username,Password,Class,Status) values(?,?,?,?)');
     var result=await query.execute([username,password,userClass,'tea']);
  +  print('${result.insertId}');//如果插入成功，这会是0，否则会报错
   }
   
   
  
positive.code:   //todo 将数据存入数据库
    var pool=new ConnectionPool(host:'localhost',port:3306,user:'root',db:'vocabulary',max:5);
    var query=await pool.prepare('insert into userinfo(Username,Password,Class,Status) values(?,?,?,?)');
    var result=await query.execute([username,password,userClass,'stu']);
  }
  
  responseTeaSignUp(request) async{
    //todo 将教师的注册信息写入数据库
    request.readAsString().then(insertDataBaseTea);
    //
    return (new Response.ok('success!',headers: _headers));
  }
  
  
negative.code: ///
  responseStuSignUp(request) async{
    //todo
    var responseDBText=await request.readAsString().then(insertDataBaseStu);
    //
    print(responseDBText);
    return (new Response.ok('success!',headers: _headers));
  }
  insertDataBaseStu(data) async{
    String username;
    String userClass;
    String password;
    String responseText;
    Map realdata=JSON.decode(data);
    username=realdata['Username'];
    userClass=realdata['Class'];
  