Question

This is an example out of a book using northwind database. What is the => mean ?

   Northwind db = new Northwind(@"Data Source=.\SQLEXPRESS;InitialCatalog=Northwind");
   var orders = db.Customers
   .Where(c => c.Country == "USA" && c.Region == "WA")
   .SelectMany(c => c.Orders);
    Console.WriteLine(orders.GetType());

why don’t they just write

   Where(c.Country == "USA" && c.Regian == "WA")

Answer 1

The part inside the parentheses of the Where() needs to be a function that takes a Customer and returns a boolean value (that’s Func<Customer, bool> in C#’s type system).

It’s most common to write that function using C#’s Lambda Expressions.

The c => part means “take the Customer that’s passed in to you and call it c. Then with that value of c, compute this conditional. Without the c on the left side of the =>, the compiler would have no way of knowing what c refers to.