CODEWITHSUNDEEP
c#.netlinq.net-4.5
simbada
simbada

Reputation: 980

handling no result found

Following line throw exception if there is no matching record found.

Guid stuId= context.Students.FirstOrDefault(x => x.Name == student.Name).Id;

I understand, i can handle above line 

var stuId= context.Students.FirstOrDefault(x => x.Name == student.Name);
if (stuId){}else{}

But,

Can i make the same line more smarter to handle no sequence found error 

Guid stuId= context.Students.FirstOrDefault(x => x.Name == student.Name).Id;

Upvotes: 0

Views: 411

Answers (4)

Tim Schmelter
Tim Schmelter

Reputation: 460208

Yes, with the null-propagation/conditional operator(new in C#6):

Guid? stuId = context.Students.FirstOrDefault(x => x.Name == student.Name)?.Id;

Now you have a nullable and it's easy to check if there is an id or not:

if(stuId.HasValue)
{
    // ...
}

If you can't use C#6 as commented:

Guid stuId = context.Students
    .Where(x => x.Name == student.Name)
    .Select(x=> x.Id)
    .DefaultIfEmpty(Guid.Empty)
    .First();

Now you can check against Guid.Empty:

if(stuId != Guid.Empty)
{

}

If Guid.Empty is a valid value you could also use a Guid? here:

Guid? stuId = context.Students
    .Where(x => x.Name == student.Name)
    .Select(x=> (Guid?) x.Id)
    .DefaultIfEmpty(null)
    .First();

Upvotes: 2

kiziu
kiziu

Reputation: 1130

If you want a solution working in lower version of C# than 6 (not using null-conditional operator), you can use cast operator like this:

var stuId = context.Students.Where(x => x.Name == student.Name).Select(i => (Guid?)i.Id).FirstOrDefault();

This will correctly return null if no record is found, as null is a default value for nullable structs.

Upvotes: 0

Ian
Ian

Reputation: 34509

I think you should be able to use the new Null Conditional Operater like so:

Guid? stuId= context.Students.FirstOrDefault(x => x.Name == student.Name)?.Id;

You can read about this new syntax in C#6 on MSDN. Basically in addition the additional question mark, it will check that the statement before isn't null before executing the right hand side. If it is it'll return a null value so you need to make your Guid nullable.

Upvotes: 3

Thomas Schmidt
Thomas Schmidt

Reputation: 379

You could do it like this:

Guid? stuId = context.Students.FirstOrDefault(x => x.Name == student.Name)?.Id;
if ( stuId.HasValue )
{
    // do something if we have a value
}

Which is using the null conditional operator, but you still need to check if you actually got a value before trying to use the value

Upvotes: 0

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