Chuyên đề phát triển phần mềm LINQ remoting ppt

Week 4: LINQ • Basic concepts – LINQ requirements – Concepts • Types – LINQ to objects – LINQ to SQL – LINQ to Entity – LINQ to XML 2. New features in langauge • 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; 2.1 Implicitly Typed Variables • Implicitly Typed Variables – Declare variables without specifying their type – Strongly type, not variant, not object – VS will determinr type • Predict what the compiler will choose • Intellisense support – Type inference -> most general • “3/10/2010” -> string, not date 2.1 Implicitly Typed Variables • Example var x = new OledbConnection(); 2.1 Implicitly Typed Variables • Note – Alwayls 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 • Usefull in any context – Especially userfull in LINQ expressions 2.2 Object Initializers • Example 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 2.3 Anonymous Types • When to user anonymous types – Need a temporary object to hold related data – Don’t need method – If we need a different set of properties for each declaration – If we need to change the order of properties for each declaration [...]... namespaces • can be extended to support other data domains 3 What is LINQ: Everywhere • LINQ to Objects, LINQ to SQL, and LINQ to XML • LINQ is an extendable technology – open-source product: LINQExtender • build your own LINQ extensions • Other providers 3 What is LINQ: Everywhere 3 LINQ • new features of.NET framework support for LINQ: – Extension methods, lambda expressions • are used extensively... syntax used in LINQ is called a query expression • provides a set of standard query operators • common tasks: query, ordered, grouped oraggregated from an existing in-memory collection, a database, an XML file or many other sources 1 What is LINQ • How LINQ works? – compiler generates code • More detail: later 1 What is LINQ: Language Integration • Language in query expression 1 What is LINQ: LINQ Flavors... example 2.4.a delegate: turn back to example: lambda 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 3 LINQ example 1 3 LINQ requirements • Net framework 3.5 • VS 2008 • Work with VS 2005: not recommended – C# – VB.NET 3 What is LINQ • a programming model that introduces queries... extensively to build queries – anonymous types : to allow data to be returned from a query without the need to first define a class or structure, – generics : creation of various types of collection 3 LINQ basic • 2 types of Syntax – Query syntax – Method syntax . Week 4: LINQ • Basic concepts – LINQ requirements – Concepts • Types – LINQ to objects – LINQ to SQL – LINQ to Entity – LINQ to XML 2. New features. Alwayls declare the type if we know – Implicitly Typed Variables are suited for LINQ and anonymous type 2.2 Object Initializers • Constructor • Allow to assign