c# - 由于对象的当前状态，操作无效。在 C#

Question

我创建了这个方法来检查表中这条记录的数量但是当 count(*) 的值为 0 时，它会给我这个错误信息我使用这个库来连接 oracle db

使用 Oracle.DataAccess.Client；

 private int checkPort(int portID)
        {
            int intCount = 0;
            try
            {
                OracleCommand oraCommand = new OracleCommand();
                oraCommand.Connection = new DBManager().getConnection();
                oraCommand.CommandText = "select count(*) as num from wireless_port_oid where port_id=:port_id";
                oraCommand.Parameters.Add(":port_id", portID);

                OracleDataReader Reader= oraCommand.ExecuteReader();


                return intCount;
                while (**Reader.Read()**)//it gives exception here
//The err Operation is not valid due to the current state of the object.
                {  
                    intCount =Convert.ToInt32(Reader[0]);
                    Reader.Close();
                    oraCommand.Connection.Close();
                    oraCommand = null;
                    if (intCount > 0)
                    {
                        return 1;
                    }
                }
                Reader.Close();
                Reader.Dispose();
                oraCommand.Connection.Close();
                oraCommand.Connection.Dispose();
                oraCommand.Dispose();
                return 0;

            }
            catch (OracleException exception)
            {
                Console.WriteLine(exception.Message);
                return 0;
            }
        }

Answer 1

您在 Count = 0 时关闭读取器，然后尝试在 while 循环中再次读取它。

while (Reader.Read())//it gives exception here
//The err Operation is not valid due to the current state of the object.
                {  
                    intCount =Convert.ToInt32(Reader[0]);
                    Reader.Close();
                    oraCommand.Connection.Close();
                    oraCommand = null;
                    if (intCount > 0)
                    {
                        return 1;
                    } 
                    // if intCOunt == 0 then what? loop again
                }

但是您的代码无效 - 我刚刚注意到您有一个 return intCount;就在您所说的行之前有错误。我认为这只是示例错字。

我会重构您的代码以利用 C# 的 using 语句:

private int checkPort(int portID) {
    string sql = "select count(*) as num from wireless_port_oid where port_id=:port_id";
    int intCount = 0;
    try {
        using(OracleCommand oraCommand = new OracleCommand()) {
            using(oraCommand.Connection = new DBManager().getConnection()) {
                oraCommand.CommandText = sql;
                oraCommand.Parameters.Add(":port_id", portID);
                intCount = oraCommand.ExecuteScalar();
            }
        }
    }
    catch (OracleException exception) {
        Console.WriteLine(exception.Message);
            // may be you shouldn't return 0 here possibly throw;
    }

    return intCount;
}