0 
    void ExecuteContent()
{
    StringBuilder sb = new StringBuilder();
    sb.Append("SELECT TOP 1 @UsersID,u.Avatar,t.Date, u.Name, t.ThreadTitle, t.ThreadParagraph");
     sb.Append(" FROM Users as u");
     sb.Append(" INNER JOIN Threads as t ON u.UsersID = t.UsersID");
     sb.Append(" Where @UsersID=t.UsersID");
     sb.Append(" ORDER BY t.Date DESC");


     using (SqlConnection conn = new SqlConnection(AnswerQuestion.connectionString))
     {
         conn.Open();
         SqlCommand sqlComm = new SqlCommand(sb.ToString(), conn);
        MembershipUser CurrentUser = Membership.GetUser();    
         Guid i = (Guid)CurrentUser.ProviderUserKey;
         sqlComm.Parameters.Add("@UsersID", SqlDbType.UniqueIdentifier).Value = i;
         SqlDataReader dr = sqlComm.ExecuteReader();

         UserName = dr["Name"].ToString();//The exception is thrown here
         Image = (Image) dr["Avatar"];
         ThreadTitle = dr["ThreadTitle"].ToString();
         ThreadParagraph = dr["ThreadParagraph"].ToString();
         Time = (DateTime)AllQuestionsPresented.TryParse(dr["Date"].ToString()); 
     }

}

我不明白为什么我得到它。我要做的就是让最后一个发布线程的人..我查看了调试，一切似乎都很好。我还查看了 Visual Studio 2010 中的 sql 服务器 .. 有数据，但不知何故它没有被读取并且抛出异常...... :(

4

2 回答 2

2

您应该在访问值之前检查 dr.Read() ：

if(dr.Read())
{
    UserName = dr["Name"].ToString();//The exception is thrown here
    Image = (Image) dr["Avatar"];
    ThreadTitle = dr["ThreadTitle"].ToString();
    ThreadParagraph = dr["ThreadParagraph"].ToString();
    Time = (DateTime)AllQuestionsPresented.TryParse(dr["Date"].ToString());
}
于 2011-06-12T17:02:02.383 回答
0

你必须通过你的阅读器循环：

while(dr.Read())
{
    serName = dr["Name"].ToString();//The exception is thrown here
         Image = (Image) dr["Avatar"];
         ThreadTitle = dr["ThreadTitle"].ToString();
         ThreadParagraph = dr["ThreadParagraph"].ToString();
         Time = (DateTime)AllQuestionsPresented.TryParse(dr["Date"].ToString()); 
}

或者if(dr.Read())如果你只有一个结果

而且您应该始终使用以下方法围绕您的 Reader：

using(dr)
{
    while(dr.Read())
    {
    }
}

你应该在调用 ToString(); 之前做一些空检查。

ThreadParagraph = dr["ThreadParagraph"] == null ? "" : dr["ThreadParagraph"].ToString();

这里有一个在代码中编写查询的小技巧，逐字逐句：

var query = @"SELECT TOP 1 @UsersID,u.Avatar,t.Date, u.Name, t.ThreadTitle, t.ThreadParagraph 
    FROM Users as u 
    INNER JOIN Threads as t ON u.UsersID = t.UsersID 
    Where @UsersID=t.UsersID ORDER BY t.Date DESC";
于 2011-06-12T17:02:05.543 回答