CODEWITHSUNDEEP
c#nullreferenceexception
jason
jason

Reputation: 7164

Null Reference exception in FirstOrDefault C#

I have this line:

myobject.Ada = result.FirstOrDefault(m => m.Name == "Ada No").Value;

Sometimes result doesn't have "Ada No" and I get

Object reference not set to an instance of an object.

I wrote an if statement to avoid null reference exception : 

if(result.FirstOrDefault(m => m.Name == "Ada No").Value != null)
{
   myobject.Ada = result.FirstOrDefault(m => m.Name == "Ada No").Value;
}

But it didn't work either. How can I avoid this exception in this piece of code? How can I write if Ada No exists, work, if not don't work? Thanks.

Upvotes: 0

Views: 3674

Answers (2)

Dom84
Dom84

Reputation: 864

The other solution would be to check with Any if any member is existing that consists of Name equal to "Ada No"

Be aware that result isn't null either!

But the null propagation way would be less to write, so it depends on you preference how you want to read your code and if it is some performance critical piece of code

if(result != null && result.Any(m => m.Name == "Ada No"))
{
    myobject.Ada = result.FirstOrDefault(m => m.Name == "Ada No").Value;
}

Upvotes: 2

Farhad Jabiyev
Farhad Jabiyev

Reputation: 26635

FirstOrDefault will return null if there is not any object which meets the condition. And the exception will be thrown when the code is trying to access a member of a reference type variable that is set to null. So, you must check if the object's value is null or not before accessing it.

You can use null-propagation operator if you are using C# 6.0:

myobject.Ada = result.FirstOrDefault(m => m.Name == "Ada No")?.Value;

Or if you are using lower versions:

var firstObj = result.FirstOrDefault(m => m.Name == "Ada No");

if(firstObj != null)
{
    myobject.Ada = firstObj.Value;
}

Upvotes: 8

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