OracleDataReader 出错.错误:无效的操作.连接已关闭 [英] Error with OracleDataReader. Error: Invalid operation. The connection is closed

问题描述

当我尝试分配读取器时，C# 抛出异常:

When I try to assign the reader C# throws an exception:

无效操作.连接已关闭

我尝试从返回单个单元格的查询中获取结果，其中包含平均值.cmd 是一个 oraclecomand，我用来在表中插入一行，到目前为止一切顺利.我看到旁边的消息框，然后出现异常.

I try to get a result from a query that returns a single cell with an average value inside. cmd is an oraclecomand that i use to insert a row into a table and so far so good. I see the message box next and after that the exception appears.

          try
            {
                cmd.ExecuteNonQuery();
                MessageBox.Show("Recipe Rated");
                OracleCommand cm = new OracleCommand("select round(avg(rating),1) from rates where id_rec = "+id);
                OracleDataReader reader = cm.ExecuteReader();
                reader.Read();
                textBox5.Text =""+reader.GetInt16(0);
            }

推荐答案

当您使用 `OracleCommand'，您必须关联一个有效的OracleConnection 对象.

When you use `OracleCommand', you have to associate a valid OracleConnection object to it.

  using (OracleConnection connection = new OracleConnection(connectionString))
    {
                   MessageBox.Show("Recipe Rated");
                   OracleCommand cm = new OracleCommand("select round(avg(rating),1) from rates where id_rec = "+id);
                   try
                    {

                        cm.Connection = connection;
                        connection.Open(); //oracle connection object
                        OracleDataReader reader = cm.ExecuteReader();
                        reader.Read();
                        textBox5.Text =""+reader.GetInt16(0);
                    }
   }

希望对您有所帮助.

谢谢.

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