LINQ Method Syntax

1. LINQ Method Syntax

2. Standard Query Operators • At compile time, query expressions which use the query syntax are translated into method calls. • These methods are called the standard query operators. Some examples are: • Where • Select • GroupBy • Join • Min, Max, Average • You can call them directly by using method syntax instead of query syntax.

3. static void Main() { int[] numbers = { 5, 10, 8, 3, 6, 12}; //Query syntax: IEnumerable<int> numQuery1 = from num in numbers where num % 2 == 0 orderbynum select num; //Method syntax: IEnumerable<int> numQuery2 = numbers .Where(num => num % 2 == 0) .OrderBy(n => n); foreach (inti in numQuery1) { Console.Write(i + " "); } Console.WriteLine(System.Environment.NewLine); foreach (inti in numQuery2) { Console.Write(i + " "); } } }

4. Lamda Expressions • The inline highlighted expression is called a lambda expression. • In C# => is the lambda operator, which is read as "goes to". • The num on the left of the operator is the input variable which corresponds to num in the query expression. • The "return value" is just the expression result. IEnumerable<int> numQuery2 = numbers.Where(num => num % 2 == 0).OrderBy(n => n);

5. Type Inference in Lambdas • Often the type of the input parameters does not have to be specified because the compiler can infer the type. • For most of the standard query operators, the first input is the type of the elements in the source sequence. • So if you are querying an IEnumerable<Customer>, then the input variable is inferred to be a Customer object, which means you have access to its methods and properties: customers.Where(c => c.City == "London");

6. Composability of Queries IEnumerable<int> numQuery2 = numbers.Where(num => num % 2 == 0).OrderBy(n => n); • The OrderBy method is invoked by using the dot operator on the call to Where. • Where produces a filtered sequence, and then Orderby operates on that sequence by sorting it. • Because queries return an IEnumerable, you compose them in method syntax by chaining the method calls together.

7. //Query syntax IQuerable<ProductType> etType = from t in entities.ItemTypes where t.ID == ID select new ProductType { ID = t.ID, TypeName = t.TypeName }; //method syntax IQuerable<ProductType> etType = entities.ItemTypes .Where(t => t.ID == ID) .Select(t => new ProductType() { ID = t.ID, TypeName = t.TypeName } );