Searching if value exists in a list of objects using Linq

Question

Say I have a class Customer which has a property FirstName. Then I have a List.

Can LINQ be used to find if the list has a customer with Firstname = 'John' in a single statement.. how?

Answer 1

LINQ defines an extension method that is perfect for solving this exact problem:

using System.Linq;
...
    bool has = list.Any(cus => cus.FirstName == "John");

make sure you reference System.Core, that's where LINQ lives.

Answer 2

customerList.Any(x=>x.Firstname == "John")

Answer 3

List<Customer> list = ...;
Customer john = list.SingleOrDefault(customer => customer.Firstname == "John");

john will be null if no customer exists with a first name of "John".

Answer 4

zvolkov's answer is the perfect one to find out if there is such a customer. If you need to use the customer afterwards, you can do:

Customer customer = list.FirstOrDefault(cus => cus.FirstName == "John");
if (customer != null)
{
    // Use customer
}

I know this isn't what you were asking, but I thought I'd pre-empt a follow-on question :) (Of course, this only finds the first such customer... to find all of them, just use a normal where clause.)

Answer 5

Another possibility

if (list.Count(customer => customer.Firstname == "John") > 0) {
 //bla
}

Answer 6

Using Linq you have many possibilities, here one without using lambdas:

//assuming list is a List<Customer> or something queryable...
var hasJohn = (from customer in list
         where customer.FirstName == "John"
         select customer).Any();

Answer 7

One option for the follow on question (how to find a customer who might have any number of first names):

List<string> names = new List { "John", "Max", "Pete" };
bool has = customers.Any(cus => names.Contains(cus.FirstName));