的ExecuteScalar引发的NullReferenceException [英] ExecuteScalar throws NullReferenceException

问题描述

这code抛出一个的NullReferenceException 时，它调用的ExecuteScalar ：

  selectedPassengerID = 0;//的SqlCommand命令= GenericDataAccess.CreateCommand（）;
//第二次测试
字符串的connectionString =;
康涅狄格州的SqlConnection;的connectionString = ConfigurationManager中。
    的ConnectionStrings [ConnST-MHM]的ConnectionString。
康恩=新的SqlConnection（的connectionString）;
的SqlCommand命令=新的SqlCommand（）;
command.CommandType = CommandType.StoredProcedure;
command.Connection =康恩;
command.CommandText =SearchForPassenger;的SqlParameter参数;参数= command.CreateParameter（）;
param.ParameterName =@name;
param.Value = PNAME; //会议（）;
param.DbType = DbType.String;
command.Parameters.Add（参数）;参数= command.CreateParameter（）;
param.ParameterName =@flightDate;
param.Value =日期;
param.DbType = DbType.String;
command.Parameters.Add（参数）;参数= command.CreateParameter（）;
param.ParameterName =@ticketNo;
param.Value = ticketNumber;
param.DbType = DbType.Int32;
command.Parameters.Add（参数）;INT项目;command.Connection.Open（）;
项目=（INT）command.ExecuteScalar（）;
 

解决方案

我已经封装在一个DAL我的大多数SQL逻辑。其中的一个方法，DAL拉使用以下逻辑标量整型。它可能为你工作：

 对象TEMP = cmnd.ExecuteScalar（）;
  如果（（临时== NULL）||（临时== DBNull.Value））返回-1;
  回报（INT）温度;
 

我知道你已经进入了很多code以上，但我认为这真的是你的问题的实质。祝你好运！

This code throws a NullReferenceException when it calls ExecuteScalar:

selectedPassengerID = 0;

//SqlCommand command = GenericDataAccess.CreateCommand();


// 2nd test
string connectionString = "";
SqlConnection conn;

connectionString = ConfigurationManager.
    ConnectionStrings["ConnST-MHM"].ConnectionString;
conn = new SqlConnection(connectionString);
SqlCommand command = new SqlCommand();
command.CommandType = CommandType.StoredProcedure ;
command.Connection = conn;
command.CommandText = "SearchForPassenger";

SqlParameter param;

param = command.CreateParameter();
param.ParameterName = "@name";
param.Value = pName; // Session[""];
param.DbType = DbType.String;
command.Parameters.Add(param);

param = command.CreateParameter();
param.ParameterName = "@flightDate";
param.Value = date; 
param.DbType = DbType.String;
command.Parameters.Add(param);

param = command.CreateParameter();
param.ParameterName = "@ticketNo";
param.Value = ticketNumber; 
param.DbType = DbType.Int32;
command.Parameters.Add(param);

int item;

command.Connection.Open();
item = (int)command.ExecuteScalar();

解决方案

I have encapsulated most of my SQL logic in a DAL. One of these DAL methods pulls scalar Ints using the following logic. It may work for you:

  object temp = cmnd.ExecuteScalar();
  if ((temp == null) || (temp == DBNull.Value)) return -1;
  return (int)temp;

I know that you have entered a lot of code above but I think that this is really the essence of your problem. Good luck!

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