C# – Select single item from a list

clinq

Using LINQ what is the best way to select a single item from a list if the item may not exists in the list?

I have come up with two solutions, neither of which I like. I use a where clause to select the list of items (which I know will only be one), I can then check the count and make a Single call on this list if count is one, the other choice is to use a foreach and just break after getting the item.

Neither of these seem like a good approach, is there a better way?

Best Answer

You can use IEnumerable.First() or IEnumerable.FirstOrDefault().

The difference is that First() will throw if no element is found (or if no element matches the conditions, if you use the conditions). FirstOrDefault() will return default(T) (null if it's a reference type).

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C# – How would you do a “not in” query with LINQ

You want the Except operator.

var answer = list1.Except(list2);

Better explanation here: https://docs.microsoft.com/archive/blogs/charlie/linq-farm-more-on-set-operators

NOTE: This technique works best for primitive types only, since you have to implement an IEqualityComparer to use the Except method with complex types.

C# – How to do joins in LINQ on multiple fields in single join

var result = from x in entity
   join y in entity2 on new { x.field1, x.field2 } equals new { y.field1, y.field2 }

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