将参数值从 SqlParameter 转换到 String 失败

Question

为什么将参数值从 SqlParameter 转换到 String 失败?存储过程如下：create  
 proc Proc_UpdateRI  
(  
  @startendTime nvarchar(50),  
  @school nvarchar(50),  
  @credential nvarchar(50)  
 )  
as  
update tb_resume  
set startendTime=@startendTime,workPlace=@school,degree=@credential  
  
 代码是这样写的：
 public void UpdateResumeInfo(string startDendtime,string school,string credential)
    {
        SqlConnection con = db.GetConnection();
        SqlCommand cmd = new SqlCommand("Proc_UpdateRI", con);
        cmd.CommandType = CommandType.StoredProcedure;
     
        SqlParameter parmTime = new SqlParameter(@startDendtime, SqlDbType.NVarChar, 50);
        parmTime.Value = startDendtime;
        cmd.Parameters.Add(parmTime);        SqlParameter paramSchool = new SqlParameter(@school, SqlDbType.NVarChar, 50);
        paramSchool.Value = school;
        cmd.Parameters.Add(paramSchool);        SqlParameter paramCredential = new SqlParameter(@credential, SqlDbType.NVarChar, 50);
        paramCredential.Value = paramCredential;
        cmd.Parameters.Add(paramCredential);        con.Open();
            try
            {
                cmd.ExecuteNonQuery();
            }catch{
              cmd.Dispose();
              con.Close();
            }
   }

Answer 1

public void UpdateResumeInfo(string startDendtime,string school,string credential) 
    { 
        SqlConnection con = db.GetConnection(); 
        SqlCommand cmd = new SqlCommand("Proc_UpdateRI", con); 
        cmd.CommandType = CommandType.StoredProcedure; 
    
        SqlParameter parmTime = new SqlParameter("@startDendtime", SqlDbType.NVarChar, 50); 
        parmTime.Value = startDendtime; 
        cmd.Parameters.Add(parmTime);         SqlParameter paramSchool = new SqlParameter("@school", SqlDbType.NVarChar, 50); 
        paramSchool.Value = school; 
        cmd.Parameters.Add(paramSchool);         SqlParameter paramCredential = new SqlParameter("@credential", SqlDbType.NVarChar, 50); 
        paramCredential.Value = paramCredential; 
        cmd.Parameters.Add(paramCredential);         con.Open(); 
            try 
            { 
                cmd.ExecuteNonQuery(); 
            }catch{ 
              cmd.Dispose(); 
              con.Close(); 
            } 
  }忘记加引号了吧