Question

Why do I get the following error in the following code?

I thought if I put custom objects in a generic List of its type then IEnumerable would be taken care of? What else do I need to do to this List to use LINQ on it?

Cannot implicitly convert type ‘System.Collections.Generic.IEnumerable<TestLinq23.Customer>‘ to ‘TestLinq23.Customer’

using System; using System.Collections.Generic; using System.Linq;  namespace TestLinq23 {     class Program     {         static void Main(string[] args)         {             List<Customer> customerSet = new List<Customer>();             customerSet.Add(new Customer { ID = 1, FirstName = 'Jim', LastName = 'Smith' });             customerSet.Add(new Customer { ID = 2, FirstName = 'Joe', LastName = 'Douglas' });             customerSet.Add(new Customer { ID = 3, FirstName = 'Jane', LastName = 'Anders' });              Customer customerWithIndex = customerSet[1];             Console.WriteLine('Customer last name gotten with index: {0}', customerWithIndex.LastName);              Customer customerWithLinq = from c in customerSet                            where c.FirstName == 'Joe'                            select c;             Console.WriteLine(customerWithLinq.LastName);              Console.ReadLine();         }     }      public class Customer     {         public int ID { get; set; }         public string FirstName { get; set; }         public string LastName { get; set; }     }  } 

Answer 1

You need to add a call to Single() – otherwise it’s returning a sequence of customers.

At the same time, there’s no real need to use a query expression here. It’ll be simpler to use dot notation:

Customer customerWithLinq = customerSet.Where(c => c.FirstName == 'Joe')                                        .Single(); 

In fact, you can make it even simpler, because there’s an overload of Single() to take a predicate:

Customer customerWithLinq = customerSet.Single(c => c.FirstName == 'Joe') 

Is it an error condition if there isn’t exactly one match? If not, you might want to use First() instead of Single().

EDIT: As pointed out by Garry, if there may be no results you might want SingleOrDefault() or FirstOrDefault() – both of these will return null if no entries match.