如何使用c＃从sql的Integer类型列中获取Null值

Question

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;
using System.Text;

namespace ConsoleApplication2
{
    class Program
    {


        static void Main(string[] args)
        {
            int? a = null;
            String connectionString = @"server=LT-1113\SQL2016;database=Employee;user=sa;password=envision1!";
            Dictionary<int,String> d = new Dictionary<int,string>();
            List<KeyValuePair<int?, String>> l = new List<KeyValuePair<int?, String>>();
            using(SqlConnection con = new SqlConnection(connectionString))
            {
                con.Open();
                SqlCommand cmd = new SqlCommand("select id,Name from details", con);
                SqlDataReader reader = cmd.ExecuteReader();
                while(reader.Read())
                {
                   // Employee e = new Employee();
                    Console.WriteLine(reader.GetValue(0));

                    int id =(int)reader.GetInt32(0);//getting exception in this line
                   // if(reader.IsDBNull(id))

                  String  Name = reader.GetValue(1).ToString();
                  l.Add(new KeyValuePair<int?,string>(id,Name) );
                }
                Console.WriteLine("Enter the Key");
                bool b = false;
                int mykey = Convert.ToInt32(Console.ReadLine());
                String Value="";
                foreach (KeyValuePair<int?, String> i in l)
                {
                    if(i.Key == mykey)
                    {
                       Value=i.Value;
                        b = true;
                    }


                   // Console.WriteLine(i.Value);

                }
                if(b==true)
                {
                    Console.WriteLine(Value);
                }
                else
                {
                    Console.WriteLine("SORRY DATA NOT PRESENT");
                }
                //Console.ReadLine();
            }
        }
    }
}
//this the code part

// **

strong text

---

****我的表具有列ID，并且将一行命名为varchar（20）name =“ ABC”和int id =“ NULL” **请先帮助我，谢谢****我的表具有列ID，并将名称行命名为varchar（20）name =“ ABC”和int id =“ NULL” **请先帮助我，谢谢****我的表具有列ID，并将一行命名为varchar（20）name =“ ABC”和int id =“ NULL” **请先帮助我，谢谢

Answer 1

通过指定IsDBNull尝试columnname

int id = reader.IsDBNull("id") ? 0 : reader.GetInt32(reader.GetOrdinal("id"))