asp.net - ExecuteScalar 抛出 NullReferenceException

Question

此代码在调用 ExecuteScalar 时抛出 NullReferenceException:

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();

Answer 1

我已将大部分 SQL 逻辑封装在 DAL 中。其中一种 DAL 方法使用以下逻辑提取标量整数。它可能适合你:

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

我知道您在上面输入了很多代码，但我认为这确实是您问题的本质。祝你好运!