C# 检查空值的最短方法，如果不是，则分配另一个值
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Shortest way to check for null and assign another value if not
提问by Splashlin
I am pulling varcharvalues out of a DB and want to set the stringI am assigning them to as "" if they are null. I'm currently doing it like this:
我正在varchar从数据库中提取值并希望将string我分配给它们的值设置为 "" 如果它们是null. 我目前正在这样做：
if (string.IsNullOrEmpty(planRec.approved_by) == true)
this.approved_by = "";
else
this.approved_by = planRec.approved_by.toString();
There seems like there should be a way to do this in a single line something like:
似乎应该有一种方法可以在一行中执行此操作，例如：
this.approved_by = "" || planRec.approved_by.toString();
However I can't find an optimal way to do this. Is there a better way or is what I have the best way to do it?
但是，我找不到执行此操作的最佳方法。有没有更好的方法，或者我有什么最好的方法来做到这一点？
采纳答案by Andrew Hare
Try this:
尝试这个：
this.approved_by = IsNullOrEmpty(planRec.approved_by) ? "" : planRec.approved_by.toString();
You can also use the null-coalescing operator as other have said - since no one has given an example that works with your code here is one:
您也可以像其他人所说的那样使用空合并运算符 - 因为没有人给出适用于您的代码的示例，这里是一个：
this.approved_by = planRec.approved_by ?? planRec.approved_by.toString();
But this example only works since a possible value for this.approved_byis the same as one of the potential values that you wish to set it to. For all other cases you will need to use the conditional operator as I showed in my first example.
但此示例仅有效，因为 的可能值this.approved_by与您希望将其设置为的潜在值之一相同。对于所有其他情况，您将需要使用我在第一个示例中展示的条件运算符。
回答by Dave Ward
The coalesce operator (??)is what you want, I believe.
该COALESCE操作符（??）是你想要的，我相信。
回答by JaredPar
You are looking for the C# coalesce operator: ??. This operator takes a left and right argument. If the left hand side of the operator is null or a nullable with no value it will return the right argument. Otherwise it will return the left.
您正在寻找 C# 合并运算符：??。此运算符采用左参数和右参数。如果运算符的左侧为 null 或一个没有值的可空值，它将返回正确的参数。否则它将返回左侧。
var x = somePossiblyNullValue ?? valueIfNull;
回答by Dmitri Nesteruk
My guess is the best you can come up with is
我的猜测是你能想到的最好的办法是
this.approved_by = IsNullOrEmpty(planRec.approved_by) ? string.Empty
: planRec.approved_by.ToString();
Of course since you're hinting at the fact that approved_byis an object(which cannot equal ""), this would be rewritten as
当然，由于您暗示的approved_by是一个事实object（不能等于“”），这将被重写为
this.approved_by = (planRec.approved_by ?? string.Empty).ToString();
回答by Paul Alexander
To extend @Dave's answer...if planRec.approved_by is already a string
扩展@Dave的答案......如果 planRec.approved_by 已经是一个字符串
this.approved_by = planRec.approved_by ?? "";
回答by user133371
You can also do it in your query, for instance in sql server, google ISNULLand CASEbuilt-in functions.
您也可以在查询中执行此操作，例如在 sql server、googleISNULL和CASE内置函数中。
回答by Ali Humayun
I use extention method SelfChk
我使用扩展方法 SelfChk
static class MyExt {
//Self Check
public static void SC(this string you,ref string me)
{
me = me ?? you;
}
}
Then use like
然后使用像
string a = null;
"A".SC(ref a);
回答by Malcolm
With C#6 there is a slightly shorter way for the case where planRec.approved_by is not a string:
在 C#6 中，对于 planRec.approved_by 不是字符串的情况，有一种更短的方法：
this.approved_by = planRec.approved_by?.ToString() ?? "";
回答by Ramgy Borja
Use the C# coalesce operator: ??
使用 C# 合并运算符： ??
// if Value is not null, newValue = Value else if Value is null newValue is YournullValue
var newValue = Value ?? YourNullReplacement;
回答by Hyman Miller
To assign a non-empty variable without repeating the actual variable name (and without assigning anything if variable is null!), you can use a little helper method with a Actionparameter:
要在不重复实际变量名称的情况下分配非空变量（如果变量为空，则不分配任何内容！），您可以使用一个带Action参数的小辅助方法：
public static void CallIfNonEmpty(string value, Action<string> action)
{
if (!string.IsNullOrEmpty(value))
action(value);
}
And then just use it:
然后只需使用它：
CallIfNonEmpty(this.approved_by, (s) => planRec.approved_by = s);
