LINQ - 2 Ravi Kumar C++/C# Team

A LINQ Query (once again)…

Anonymous Types! New “on the fly” class with read-only properties. var p = new { X = 0, Y = 1 }; Console.WriteLine("(X,Y) Coords = ({0},{1})", p.X, p.Y); Console.WriteLine("The typename is {0}",p.GetType().Name); <>f__AnonymousType1`2[System.Int32,System.Int32].

Query Expression! Set of clauses written in a new declarative syntax (SQL like). Starts with: From clause. Must end with: select or group clause. Type-checked. More clause: where, orderby, join. (etc..) Source of QE: IEnumerable. Returns: IEnumerable<T>

Contextual Keywords! New QE clauses. Keywords in context of QE. E.g.: From, select, etc… Keywords in context of QE. int from = 0; OK Var x = from c in customer Where c.Name == “ME” Select new {c.Name, c.Age}; Query Expression

QE -> Method Invocation List<int> scores = new List<int> { 77, 98, 92, 85, 80 }; IEnumerable<int> query = from score in scores where score >= 90 select score; Compiler translation List<int> scores = new List<int> { 77, 98, 92, 85, 80 }; var query = scores.Where(score => score >= 90).Select(score => score); where and select are ext methods in System.Linq.Enumerable namespace.

Translation of QE! Source object. (scores) where clause -> Where(…) from score in scores where score >= 90 select score; Source object. (scores) where clause -> Where(…) Parameter -> lambda exp with variable and exp in clause scores.Where( score => score >= 90) Enumerable.Where<int>( Func<int,bool>). Select clause -> Select(…)

Standard Query Operators System.Linq.Enumerable class. Example: Where(), Select(), OrderBy(), Distinct(), Average(), Max(), Min() etc… These Extension methods are collectively known as the Standard Query Operators. http://msdn2.microsoft.com/en-us/vcsharp/aa336746.aspx

Expression Trees… Data representation of the code that a C# lambda expression would execute if the expression were compiled to IL. parsing which the compiler generates executable code. Parsed code that has not been compiled to IL.

Lets LINQ Together!!