再不用擔心DataRow類型轉換和空值了（使用擴展方法解決高頻問題）

在使用DataRow讀取數據時，通常會遇到數據可能為Null, 但是又需要轉換為如int等其它類型的數據，因此就通常會寫這樣的代碼：

if (dr[name] != DBNull.Value && dr[name] != null)
{
    if (!int.TryParse(dr[name].ToString(), out result))
        throw new Exception("整形轉換失敗");
}

而且這樣的代碼通常會大段大段出現在很多地方。
對於比較懶惰的程序員來說，這樣的RY(repeat yourself)是一件很痛苦的事情，因此是時候來想個更好的方法了。這里首先想到的就是Extension Method。

很簡單的幾句代碼，有了這個方法之后，在使用DataRow時，就可以通過擴展方法讀取數據了

model.Id =  dr.SafeRead<Int32>("Id",0);
model.codeNum = dr.GetString("codeNum");

簡單但是實用的代碼，希望對大家在項目中有所幫助。

這里參考了,一下兩篇文章，並進行了代碼重新組織，最后是整理后類源碼

使用 Extension Methods 來使 IDataReader 更加方便

C#底層SqlDataReader類常用擴展

    public static class SystemDataExtension
    {
        #region DataReader 擴展
        public static T SafeRead<T>(this IDataReader reader, string fieldName, T defaultValue)
        {
            try
            {
                object obj = reader[fieldName];
                if (obj == null || obj == System.DBNull.Value)
                    return defaultValue;

                return (T)Convert.ChangeType(obj, defaultValue.GetType());
            }
            catch
            {
                return defaultValue;
            }
        }

        /// <summary>          
        /// 獲取字符串類型數據   
        /// </summary>     
        /// <param name="dr"></param>  
        /// <param name="name"></param>      
        /// <returns></returns>      
        public static string GetString(this IDataReader dr, string name)
        {

            if (dr[name] != DBNull.Value && dr[name] != null)
                return dr[name].ToString();
            return String.Empty;
        }
        /// <summary>          
        /// 獲取非空類型數據         
        /// </summary>          
        /// <param name="con"></param>
        /// <param name="name"></param>
        /// <returns></returns>        
        public static DateTime GetDateTime(this IDataReader dr, string name)
        {
            DateTime result = DateTime.Now;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!DateTime.TryParse(dr[name].ToString(), out result))
                    throw new Exception("日期格式數據轉換失敗");
            }
            return result;
        }
        /// <summary>          
        /// 獲取可空類型日期數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static DateTime? GetNullDateTime(this IDataReader dr, string name)
        {

            DateTime? result = null;
            DateTime time = DateTime.Now;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!DateTime.TryParse(dr[name].ToString(), out time))
                    throw new Exception("日期格式數據轉換失敗");
                result = time;
            }
            return result;
        }

        /// <summary>          
        /// 獲取guid類型數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static Guid GetGuid(this IDataReader dr, string name)
        {
            Guid guid = Guid.Empty;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (Guid.TryParse(dr[name].ToString(), out guid))
                    throw new Exception("guid類型數據轉換失敗");
            }
            return guid;
        }
        /// <summary>         
        /// 獲取整形數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>         
        public static int GetInt32(this IDataReader dr, string name)
        {
            int result = 0;

            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!int.TryParse(dr[name].ToString(), out result))
                    throw new Exception("整形轉換失敗");
            }
            return result;
        }

        /// <summary>         
        /// 獲取雙精度類型數據 
        /// </summary>    
        /// <param name="dr"></param>   
        /// <param name="name"></param>     
        /// <returns></returns>          
        public static double GetDouble(this IDataReader dr, string name)
        {
            double result = 0.00;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!double.TryParse(dr[name].ToString(), out result))
                    throw new Exception("雙精度類型轉換失敗");
            }
            return result;
        }
        /// <summary>          
        /// 獲取單精度類型數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static float GetSingle(this IDataReader dr, string name)
        {
            float result = 0.00f;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!float.TryParse(dr[name].ToString(), out result))
                    throw new Exception("單精度類型轉換失敗");
            }

            return result;
        }

        /// <summary>          
        /// 獲取decimal類型數據         
        /// </summary>          
        /// <param name="dr"></param>  
        /// <param name="name"></param>     
        /// <returns></returns>          
        public static decimal GetDecimal(this IDataReader dr, string name)
        {
            decimal result = 0.00m;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!decimal.TryParse(dr[name].ToString(), out result))
                    throw new Exception("Decimal類型轉換失敗");
            }
            return result;
        }

        /// <summary>          
        /// 獲取int16類型數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static Int16 GetInt16(this IDataReader dr, string name)
        {
            short result = 0;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!short.TryParse(dr[name].ToString(), out result))
                    throw new Exception("短整形轉換失敗");
            }
            return result;
        }

        /// <summary>          
        /// 獲取Byte類型數據         
        /// </summary> 
        ///  <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static byte GetByte(this IDataReader dr, string name)
        {
            byte result = 0;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!byte.TryParse(dr[name].ToString(), out result))
                    throw new Exception("Byte類型轉換失敗");
            }
            return result;
        }

        /// <summary>          
        /// 獲取bool類型數據如果傳值是1或者是返回true;        
        /// </summary>          
        /// <param name="con"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static bool GetBool(this IDataReader dr, string name)
        {
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                return dr[name].ToString() == "1" || dr[name].ToString() == "是" || dr[name].ToString().ToLower() == "true";
            }
            return false;
        } 
        #endregion

        #region DataRow 擴展
        public static T SafeRead<T>(this DataRow dr, string fieldName, T defaultValue)
        {
            try
            {
                object obj = dr[fieldName];
                if (obj == null || obj == System.DBNull.Value)
                    return defaultValue;

                return (T)Convert.ChangeType(obj, defaultValue.GetType());
            }
            catch
            {
                return defaultValue;
            }
        }

        /// <summary>          
        /// 獲取字符串類型數據   
        /// </summary>     
        /// <param name="dr"></param>  
        /// <param name="name"></param>      
        /// <returns></returns>      
        public static string GetString(this DataRow dr, string name)
        {

            if (dr[name] != DBNull.Value && dr[name] != null)
                return dr[name].ToString();
            return String.Empty;
        }
        /// <summary>          
        /// 獲取非空類型數據         
        /// </summary>          
        /// <param name="con"></param>
        /// <param name="name"></param>
        /// <returns></returns>        
        public static DateTime GetDateTime(this DataRow dr, string name)
        {
            DateTime result = DateTime.Now;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!DateTime.TryParse(dr[name].ToString(), out result))
                    throw new Exception("日期格式數據轉換失敗");
            }
            return result;
        }
        /// <summary>          
        /// 獲取可空類型日期數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static DateTime? GetNullDateTime(this DataRow dr, string name)
        {

            DateTime? result = null;
            DateTime time = DateTime.Now;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!DateTime.TryParse(dr[name].ToString(), out time))
                    throw new Exception("日期格式數據轉換失敗");
                result = time;
            }
            return result;
        }

        /// <summary>          
        /// 獲取guid類型數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static Guid GetGuid(this DataRow dr, string name)
        {
            Guid guid = Guid.Empty;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (Guid.TryParse(dr[name].ToString(), out guid))
                    throw new Exception("guid類型數據轉換失敗");
            }
            return guid;
        }
        /// <summary>         
        /// 獲取整形數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>         
        public static int GetInt32(this DataRow dr, string name)
        {
            int result = 0;

            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!int.TryParse(dr[name].ToString(), out result))
                    throw new Exception("整形轉換失敗");
            }
            return result;
        }

        /// <summary>         
        /// 獲取雙精度類型數據 
        /// </summary>    
        /// <param name="dr"></param>   
        /// <param name="name"></param>     
        /// <returns></returns>          
        public static double GetDouble(this DataRow dr, string name)
        {
            double result = 0.00;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!double.TryParse(dr[name].ToString(), out result))
                    throw new Exception("雙精度類型轉換失敗");
            }
            return result;
        }
        /// <summary>          
        /// 獲取單精度類型數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static float GetSingle(this DataRow dr, string name)
        {
            float result = 0.00f;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!float.TryParse(dr[name].ToString(), out result))
                    throw new Exception("單精度類型轉換失敗");
            }

            return result;
        }

        /// <summary>          
        /// 獲取decimal類型數據         
        /// </summary>          
        /// <param name="dr"></param>  
        /// <param name="name"></param>     
        /// <returns></returns>          
        public static decimal GetDecimal(this DataRow dr, string name)
        {
            decimal result = 0.00m;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!decimal.TryParse(dr[name].ToString(), out result))
                    throw new Exception("Decimal類型轉換失敗");
            }
            return result;
        }

        /// <summary>          
        /// 獲取int16類型數據         
        /// </summary>          
        /// <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static Int16 GetInt16(this DataRow dr, string name)
        {
            short result = 0;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!short.TryParse(dr[name].ToString(), out result))
                    throw new Exception("短整形轉換失敗");
            }
            return result;
        }

        /// <summary>          
        /// 獲取Byte類型數據         
        /// </summary> 
        ///  <param name="dr"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static byte GetByte(this DataRow dr, string name)
        {
            byte result = 0;
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                if (!byte.TryParse(dr[name].ToString(), out result))
                    throw new Exception("Byte類型轉換失敗");
            }
            return result;
        }

        /// <summary>          
        /// 獲取bool類型數據如果傳值是1或者是返回true;        
        /// </summary>          
        /// <param name="con"></param>         
        /// <param name="name"></param>         
        /// <returns></returns>          
        public static bool GetBool(this DataRow dr, string name)
        {
            if (dr[name] != DBNull.Value && dr[name] != null)
            {
                return dr[name].ToString() == "1" || dr[name].ToString() == "是" || dr[name].ToString().ToLower() == "true";
            }
            return false;
        }
        #endregion
    }