c# - 指定的演员表无效。是因为我试图投射一个物体吗？

Question

我有以下 C# 代码用于尝试查询 oracle 数据库。我只是想获得数字结果，以便可以将其输出到控制台并最终将其保存在变量中。

我不断收到以下错误：

System.InvalidCastException：指定的转换在 Oracle.DataAccess.Client.OracleDataReader.GetInt32(Int32 i) 处无效

我在 Windows 专业机器上使用 VS 2012。如果我需要添加其他信息，请告诉我。非常感谢任何帮助。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Oracle.DataAccess.Client;
using Oracle.DataAccess.Types;
using System.Configuration;
using System.Data.SqlClient;

namespace OB_837_File_Reconciliation_Rpt_Automation
{
  class Program
  {
    static void Main(string[] args)
   {
      OracleConnection dbConnection;
      string connectionString = "Data Source=(DESCRIPTION=(ADDRESS=             (PROTOCOL=TCP)(HOST=*******)(PORT=******))(CONNECT_DATA=(SERVICE_NAME=******)));User ID=*****;Password=*********";
        try
        {
            dbConnection = new OracleConnection(connectionString);                
            string query = "select count (*) AS AMG_Prof from wellmed_owner.claim c inner join WELLMED_OWNER.payment_detail pd on c.claim_id = pd.claim_id where c.claim_status in ('6','8','C') and c.insured_group_id in ('ASA','AEP') and c.form_type = '1' and trunc(pd.paid_date) = trunc(sysdate -4)";
            dbConnection.Open();
            OracleCommand comm = new OracleCommand(query, dbConnection);               
            OracleDataReader rdr = comm.ExecuteReader();
            rdr.Read();                
            int count = (int)comm.ExecuteScalar();
            Console.WriteLine(count);
            //int num = rdr.GetInt32(0);
            //Console.WriteLine(count);              
            Console.WriteLine("Connecting Okay");

       }
     catch (Exception e)
     {
       Console.WriteLine(e);
     }

        }
    }
}

Answer 1

利用ExecuteScalar

dbConnection.Open();
OracleCommand comm = new OracleCommand(query, dbConnection);               
decimal count = (decimal)comm.ExecuteScalar();
Console.WriteLine(count);              
Console.WriteLine("Connecting Okay");

Answer 2

您的查询仅返回一个值，因此请使用 ExecuteScalar 而不是 ExecuteReader。

Object result =  comm.ExecuteScalar ();
if(result != null)
{
     decimal count = (decimal) result;
}