Language Integrated Query potx

HO CHI MINH UNIVERSITY OF INDUSTRY LINQ Language Integrated Query HO CHI MINH UNIVERSITY OF INDUSTRY  Basic concepts  LINQ requirements  Concepts  Types  LINQ to objects  LINQ to SQL  LINQ to Entity  LINQ to XML 1. Basic concepts & Types LinQ HO CHI MINH UNIVERSITY OF INDUSTRY 2. New features in language:  Generics  Implicitly Typed Variables  Object Initializers  Anonymous Types  Extension Methods  Lambda Expressions HO CHI MINH UNIVERSITY OF INDUSTRY 2.0. Generics  The creation of various types of collection  Type safety  Binary Code Reuse using System.Collections.Generic; List<int> intS = new List<int>(); intS.Add(113); intS.Add(114); int nAt = intS[0]; HO CHI MINH UNIVERSITY OF INDUSTRY 2.1. Implicitly Typed Variables  Implicitly Typed Variables – Declare variables without specifying their type – Strongly type, not variant, not object – Visual Studio will determine type • Predict what the compiler will choose • Intelligence support – Type inference -> most general • “3/10/2010” -> string, not date HO CHI MINH UNIVERSITY OF INDUSTRY  Example 2.1. Implicitly Typed Variables private void button2_Click(object sender, EventArgs e) { var x = 113; var y = "1/1/2012"; var z = 1.7; var k = new DateTime(2012, 1, 1); string msg = "x type="+x.GetType() + "\n"+ "y type = "+y.GetType() + "\n" + "z type ="+z.GetType() + "\n" + "k type = " + k.GetType(); MessageBox.Show(msg); } HO CHI MINH UNIVERSITY OF INDUSTRY 2.1. Implicitly Typed Variables  Note – Always declare the type if we know – Implicitly Typed Variables are suited for LINQ and anonymous type HO CHI MINH UNIVERSITY OF INDUSTRY 2.2. Object Initializers  Constructor  Allow to assign values to object properties (fields) when create object  We do not have to explicitly invoke a constructor  Useful in any context – Especially useful in LINQ expressions HO CHI MINH UNIVERSITY OF INDUSTRY 2.2. Object Initializers  Example class Test { public int a, b; public int a2 { set;get;} public int b2 { get; set; } } private void button3_Click(object sender, EventArgs e) { var x = new Test() {a=113,b=114,a2=115,b2=116}; MessageBox.Show(x.a2+""); } HO CHI MINH UNIVERSITY OF INDUSTRY 2.3. Anonymous Types  Implicitly type functionality for objects – Set property values to object without writing class definition – The resulting class has no usable name – Class name is generated by compiler, inherits from Object – The result: an anonymous type that is not available at source code level  Also called Projections [...]... delegate: turn back to example: lambda private void btnEven_Click(object sender, EventArgs e) { listNumber.SelectItemInListBox(x => x % 2 == 0); } HO CHI MINH UNIVERSITY OF INDUSTRY 3 LINQ Language Integrated Query LINQ does create a new way of looking at enumerations of data, and gives out-of-the-box functionality for them – L2O – L2S – L2E – L2X – L2D HO CHI MINH UNIVERSITY OF INDUSTRY 3 LINQ example . HO CHI MINH UNIVERSITY OF INDUSTRY LINQ Language Integrated Query HO CHI MINH UNIVERSITY OF INDUSTRY  Basic concepts  LINQ requirements  Concepts  Types  LINQ. concepts & Types LinQ HO CHI MINH UNIVERSITY OF INDUSTRY 2. New features in language:  Generics  Implicitly Typed Variables  Object Initializers  Anonymous