防止用户注册两次

Question

我有一个注册表格，我想检查用户以前没有注册过。

我的代码在下面。我认为存在两个问题：（1）调用方法和（2）将参数传递给存储过程。我的症状是，这导致一个异常，说输入参数未初始化。

create procedure fakeuser @username nvarchar(250),@codemeli nchar(10),@email  nvarchar(50), @user nvarchar(250) output,@code nchar(10)output,@mail nvarchar(50)output 
as 
if exists(select username,email,codemeli from karbar where username=@username) 
set @user=@username 
else if exists(select username,email,codemeli from karbar where codemeli=@codemeli) 
set @code=@codemeli 
else if exists(select username,email,codemeli from karbar where email=@email) 
set @mail= @email 

下面是C＃代码：

public static string confirm(string username, string email, string codemeli) 
    { 
     string constring = "data source=.;database=site;integrated security=true;"; 
     SqlConnection connection = new SqlConnection(constring); 

     // Command - specify as StoredProcedure 
     SqlCommand command = new SqlCommand("fakeuser", connection); 
     command.CommandType = CommandType.StoredProcedure; 

     SqlParameter param = new SqlParameter("@username", SqlDbType.NVarChar); 
     param.Direction = ParameterDirection.Input; 
     param.Value = username; 
     command.Parameters.Add(param); 

     SqlParameter param2 = new SqlParameter("@email", SqlDbType.NVarChar); 
     param2.Direction = ParameterDirection.Input; 
     param2.Value = username; 
     command.Parameters.Add(param2); 

     SqlParameter param3 = new SqlParameter("@codemeli", SqlDbType.NChar); 
     param3.Direction = ParameterDirection.Input; 
     param3.Value = username; 
     command.Parameters.Add(param3); 

     // Return value as parameter 
     SqlParameter returnuser = new SqlParameter("@user", SqlDbType.NVarChar); 
     returnuser.Direction = ParameterDirection.ReturnValue; 
     command.Parameters.Add(returnuser); 

     SqlParameter returncode = new SqlParameter("@code", SqlDbType.NChar); 

     returncode.Direction = ParameterDirection.ReturnValue; 

     command.Parameters.Add(returncode); 
     SqlParameter returnmail = new SqlParameter("@mail", SqlDbType.NVarChar); 
     returnmail.Direction = ParameterDirection.ReturnValue; 
     command.Parameters.Add(returnmail); 

     // Execute the stored procedure 
     connection.Open(); 
     command.ExecuteNonQuery(); 
     connection.Close(); 

谢谢。

Answer 1

为@ user，@ code和@mail设置ParameterDirection=Output，并指定参数的宽度/大小/长度。

SqlParameter returnuser = new SqlParameter("@user", SqlDbType.NVarChar,100); 
returnuser.Direction = ParameterDirection.Output; 
command.Parameters.Add(returnuser);