LINQ ANY() with First() And FirstOrDefault()

Question

I've written code like this

TotalCashIn = totals != null && totals.Any() ? totals.First().TotalCashIn : null;

And i have been blamed for this code and have told to write like this

TotalCashIn = totals != null ? totals.FirstOrDefault().TotalCashIn : null;

But I am wondering would not I get an exception if totals count would be 0? Do I need also check this with .Any() or .Count() ?

Answer 1

You can use the null-conditional operator to make all of this a lot simpler, assuming that the element type of totals is a reference type:

TotalCashIn = totals?.FirstOrDefault()?.TotalCashIn;

With this:

• If totals is null, the overall result is null due to the first null-conditonal operator
• If totals is empty, FirstOrDefault() will return null, so the overall result is null due to the second null-conditional operator
• Otherwise, the result is the TotalCashIn property of the first element

Answer 2

It depends whether totals is IEnumerable or IQueryable . If it is IQueryable then you can also use following:

TotalCashIn = totals?.Select(t => (int?)t.TotalCashIn).FirstOrDefault();

It would be better as you select only desired field and not all columns in a table.

Answer 3

If totals is a reference type object, then indeed, FirstOrDefault might return null, and thus you can't call TotalCashIn.

If on the other hand totals is a value type, then FirstOrDefault would return an actual value and you could call TotalCashIn. For instance if totals would be a sequence of integers, then FirstOrDefault would return zero (not null!).

If TotalCashIn would be an extension function of int, then if would be perfect to call TotalCashIn after FirstOrDefault:

IEnumerable<int> totals = ...
int firstInt = totals.FirstOrDefault();
var totalCashIn = firstInt.TotalCashIn(); // extension function of int

or in one statement:

var totalCashIn = totals.FirstOrDefault().TotalCashIn();

Whether it is wise to use the null-conditional operator (?.) depends on the definition of your TotalCashIn, especially if your collection has no element at all.

If you'd say: "TotalCashIn represents the amount of money I cashed while ...", then TotalCashIn could have a zero value, but not a null value.

If you want a zero value in case of empty collections, consider to use Select to select the property you want before your FirstOrDefault:

var totalCashIn = totals.Select(item => item.TotalCashIn).FirstOrDefault();

If property TotalCashIn is a value type then this will return zero if your totals collection is empty

Upon your question whether to use Count() or Any(): never use Count() to test if your sequence has any elements unless you are certain the your input sequence is an ICollection. It is really a waste of computing power to access all elements of your sequence if after the first element you would already know there are elements.