从IDataReader获取值的空安全方法 [英] Null safe way to get values from an IDataReader

问题描述

(LocalVariable)ABC.string(Name)=(Idatareader)datareader.GetString(0);

(LocalVariable)ABC.string(Name)= (Idatareader)datareader.GetString(0);

此名称值来自数据库. 如果此名称值在读取时抛出异常，则为空?

this name value is coming from database.. what happening here is if this name value is null while reading it's throwing an exception?

我在这里手动执行一些if条件.我不想编写手动条件来检查我所有的变量.

I am manually doing some if condition here. I don't want to write a manual condition to check all my variables..

我现在正在做这样的事情.

I am doing something like this now..

string abc =  (Idatareader)datareader.GetValue(0);
if(abc = null)
    //assiging null
else
    assiging abc value

是否可以为它编写扩展方法? 谢谢

is there something like can we write extension method for this? thanks

推荐答案

以下是几种扩展方法，它们很好地总结了您从数据读取器中检索强类型值的所有问题.如果值为DbNull，则将返回该类型的默认值.如果string是一个类，则将返回null.如果该字段是int，则将返回0.此外，如果您期望int?，例如从可为null的int字段中返回，则将返回null.

Here is a couple extension methods that will nicely wrap up all of your concerns around retrieving strongly typed values from a data reader. If the value is DbNull the default of the type will be returned. In the case of string which is a class, a null will be returned. If the field was int, then 0 would be returned. Additionally, if you are expecting an int?, say from an nullable int field, null would be returned.

Kumar案件的具体用法:

Specific Usage for Kumar's case:

string abc = datareader.GetValueOrDefault<string>(0);

一般用法

var name = GetValueOrDefault<string>(reader, "Name");

或

var name = reader.GetValueOrDefault<string>("Name");

或

var name = reader.GetValueOrDefault<string>(0);

扩展名

public static class NullSafeGetter
{
   public static T GetValueOrDefault<T>(this IDataRecord row, string fieldName)
   {
       int ordinal = row.GetOrdinal(fieldName);
       return row.GetValueOrDefault<T>(ordinal);
   }

   public static T GetValueOrDefault<T>(this IDataRecord row, int ordinal)
   {
       return (T)(row.IsDBNull(ordinal) ? default(T) : row.GetValue(ordinal));
   }
}

来自 http://skysanders .net/subtext/archive/2010/03/02/generic-nullsafe-idatarecord-field-getter.aspx

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