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Bài giảng Công nghệ lập trình tiên tiến: Chương 2 - ĐH Công nghệ Đồng Nai

Bài giảng Công nghệ lập trình tiên tiến: Chương 2 trình bày các nội dung kiến thức về truy xuất dữ liệu với LINQ như các thao tác trên máy tính, câu lệnh, cú pháp,. Tham khảo nội dung bài giảng để hiểu rõ hơn về các nội dung trên. | LINQ Language Integrated Query 1 Basic concepts LINQ requirements Concepts Types LINQ to objects LINQ to SQL LINQ to Entity LINQ to XML LINQ to Dataset 1. Basic concepts & Types LinQ 2 2. New features in language: Generics Implicitly Typed Variables Object Initializers Anonymous Types Extension Methods Lambda Expressions 2.0. Generics The creation of various types of collection Type safety Binary Code Reuse using System.Collections.Generic; List intS = new List(); intS.Add(113); intS.Add(114); int nAt = intS[0]; 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 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 | LINQ Language Integrated Query 1 Basic concepts LINQ requirements Concepts Types LINQ to objects LINQ to SQL LINQ to Entity LINQ to XML LINQ to Dataset 1. Basic concepts & Types LinQ 2 2. New features in language: Generics Implicitly Typed Variables Object Initializers Anonymous Types Extension Methods Lambda Expressions 2.0. Generics The creation of various types of collection Type safety Binary Code Reuse using System.Collections.Generic; List intS = new List(); intS.Add(113); intS.Add(114); int nAt = intS[0]; 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 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); } 2.1. Implicitly Typed Variables Note – Always declare the type if we know – Implicitly Typed Variables are suited for LINQ and anonymous type 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 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+""); } 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 .