What does this LINQ query do?

Question

Here are two C# classes...

public class Address  
{  
    public string Country;  
    public string City;  
}

public class Traveller
{    
    public string Name;
    public List<Address> TravelRoute;
}

... and a list of data (filled somewhere) ...

List<Traveller> Travellers;

... and then this LINQ query:

var result = from t in Travellers
             where t.TravelRoute.Any(a => a.Country == "F")
             select t;

foreach (var t in result)
    System.Console.WriteLine(t.Name);

I do not understand the query: What means the "Any" function and what does the "=>" operator do?

Can someone explain me what's going on in this code? Thanks!

Answer 1

It selects all travelers whose TravelRoute contains a country that is "F".

The Any functions returns true if any of the objects in the list satisfies the condition that is passed in to the function. From the method signature, you can see it takes a Func<> delegate that returns a bool. This means it takes any method that will return a boolean, including the lambda expression supplied.

This is different from Where, which will filter according to the condition that is passed in.

The => is a lambda expression. In this particular case, it is a shortcut to write an anonymous delegate.

Answer 2

It's a lambda expression. http://msdn.microsoft.com/en-us/library/bb397687.aspx It looks like it's selecting all of the travelers that have any travel route in "F", which is presumably a country.

Answer 3

=> is used in C# lambdas.

Answer 4

Any is a filter method which says "Accept any items which meet the following criteria." The a => ... business means "Given a parameter a, here's a method" -- as others have said, it's used for lambda expressions. Edit: changed "property" to "parameter"

Answer 5

The line

a => a.Country == "F"

would translate to something like this if it was a separated LINQ statement:

From a as Adress in t.TravelRoute
Where a.Country = "F"
Select a

The any means it : Any. In other word, it will return true if ANY of the objects in travelRoute has its Country property to "F"

Hope that helps