Drop 'Where' and move the condition into the 'First' in LINQ

Question

I have a windows application which has some similar code as below.
As class named Order.

class Order{ public string Orderid { get; set; } public string CustName { get; set; } }

Now, in another class in this application, object for Order class is created and value is assigned to it.

Order order = new Order(); order = JObject.Parse(some JSON data).ToObject<Order>();

Now I want to extract the CustName based on Orderid from order. For this I have used LINQ.

string custName = order.Where(s => s.Key == "o123").First().Value;

I'm using Sonarqube to check the code quality. When I run the SonarQube tool , it is showing that I need to refactor my code where I have used LINQ. This is the exact line it shows.

Drop 'Where' and move the condition into the 'First'.

I have searched for it a lot but couldn't understand what it is trying to say. Can anyone explain me how to refactor this line , so that it passes the SonarQube expectations.
Any input is highly helpful.Thanks.

order.First(s => s.Key == "o123")

dymanoid
– dymanoid

2018-07-20 10:13:35 +00:00
Commented Jul 20, 2018 at 10:13 — dymanoid
– dymanoid, Commented Jul 20, 2018 at 10:13

X.Otano · Accepted Answer · 2018-07-20 10:19:35Z

You are perfoming an operation in two steps when you could do that by using the First lambda expression

string custName = order.First(s => s.Key == "o123").Value;

Linq method First definition:

First<TSource>(this IEnumerable<TSource>, Func<TSource, Boolean>)

First parameter is the IEnumerable you are using (Linq are extension methods)
Second parameter allows you to set the filter declaring a Func<TSource, Boolean> as parameter, that you could define as s => s.Key == "o123"

stuartd · Accepted Answer · 2018-07-20 18:00:17Z

What it is telling you is that the Where is unnecessary, and the code can be expressed as this:

string custName = order.First(s => s.Key == "o123").Value;

The logic of the original code is this:

"look through the list to find any matches, and take the first"

Which is the same as the changed code:

"take the first match in the list"

Note though that this code will throw an exception if there is no match. If there's ever a possibility that there will not be a matching customer, use FirstOrDefault instead:

string custName; var customer = order.FirstOrDefault(s => s.Key == "o123"); if (customer != null) { custName = customer.Value; } else { // code to handle no match }

if null is sufficient as the result when there is no match, it can be shortened to string custName = order.FirstOrDefault(s => s.Key == "o123")?.Value

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