Linq And Its Impact On The.Net Framework

LINQ and Its Impact on the .NET Framework Richard Rush

LINQ and Its Impact on the .NET Framework What is LINQ? New features that enable LINQ LINQ providers Examples

What is LINQ? L anguage IN tegrated Q uery Designed to provide a uniform way to retrieve data from different types of data stores Can query against anything that implements the IEnumerable<T> interface

New Features that Enable LINQ Extension methods Lambda expressions Anonymous constructors Anonymous fields Anonymous types and implicit typing

Extension Methods Add functionality to , or “extend,” classes you cannot alter the source code for. Every class can be extended public static [output] [Extension] (this [class] source) { // Method Body } public static string HtmlEncode(this string source) { return System.Web.HttpUtility.HtmlEncode(source); }

Lambda Expressions Anonymous Methods Work sort of like Delegates Different notation for functions Defined as (λ V. E), where: V is an identifier E is an operation, or another lambda expression x => x+2 .NET Lamba Notation λ x . x +2 Lamba Notation f ( x ) = x +2 Standard Notation

Anonymous Constructors Allow the initialization of objects and their settable properties in a single line Calls the constructor and then sets all the specified properties to the specified values No constructor overload is needed, but they can still be used Anonymous constructors can be nested

Anonymous Constructor Example p = new PersonObject() { Id = 1, RoleId = 2, FirstName = "Peter", LastName = "Parker" }; Is equivalent to: p = new PersonObject(); p.Id = 1; p.RoleId = 2; p.FirstName = “Peter”; p.LastName = “Parker”;

Anonymous Fields Implicitly define a field by explicitly defining a property

Anonymous Field Example So private string _FirstName; public string FirstName { get { return _FirstName; } set { _FirstName = value; } } and public string FirstName; become public string FirstName { get; set; }

So, now we have: Anonymous methods (Lamba Expressions) Anonymous constructors Anonymous fields What could possibly be next?

Anonymous Types and Implicit Typing Bring all of the previous enhancements together Define strongly typed classes implicitly Supported by Intellisense Locally scoped

Anonymous Type and Implicit Typing Examples var i = 5; var s = “This is a string.”; var p = new { FirstName=“Peter”, LastName=“Parker”} var x; // This won’t work. Exception time! i = “Well, what about this?”; // Nope!

How does all of this relate to LINQ?

Some Assumptions… public class Person { public string FirstName { get; set; } public int Id { get; set; } public int RoleId { get; set; } public string LastName { get; set; } public Person () { } public Person (int id) { Id = id; } } List<Person> _PeopleList = FillPeopleList();

Example: Object-Oriented Select public List<Person> SelectPerson(int id) { List<Person> output = new List<Person>(); foreach (Person currentPerson in _P eopleList) { if (currentPerson.Id == id ) { output.Add(currentPerson); } } } return output; }

Example: Object-Oriented Select with Extension Method public List<Person> SelectPerson(int id) { return _P eopleList .Where(id); } public static List<Person> Where (this List<Person> source , int id ) { List<Person> output = new List<Person>(); foreach (Person currentPerson in source ) { if (currentPerson.Id == id ) { output.Add(currentPerson); } } return output; }

Example: Object-Oriented LINQ Extension Method Use public IEnumerable<Person> SelectPerson(int id) { var query = _P eopleList.Where(p => p.Id == inputId); return query ; }

Example: LINQ public IEnumerable<Person> SelectPerson(int id) { var query = from p in _P eopleList where p.Id == inputId select p; return query ; }

Example: Object-Oriented LINQ Extension Method Use and Anonymous Types public ?????? SelectPerson(int id) { var query = _P eopleList .Where(p => p.Id == inputId) .Select(p=> new { p.FirstName, p.LastName }) ; return query ; }

Example: LINQ with Anonymous Types public ?????? SelectPerson(int id) { var query = from p in _P eopleList where p.Id == inputId select new { p.FirstName, p.LastName }; return query ; }

LINQ Providers LINQ to Objects LINQ to XML LINQ to DataSets LINQ to SQL Custom LINQ Providers

LINQ to XML public ?????? SelectPerson(int id) { XDocument peopleDoc = XDocument.Load(Server.MapPath("~/App_Data/People.xml")); var query = from p in peopleDoc.Elements("People").Elements("Person") where p.Element("Id").Value == id select new { FirstName = p.Element("FirstName").Value, LastName = p.Element("LastName").Value }; return query; }

LINQ to DataSets public ?????? SelectPerson(int id) { PeopleDataSet peopleD ata = DataAccess.GetDataSet<PeopleDataSet>("GetData", CommandType.StoredProcedure, tableMappings); var query = from p in peopleData .Person where p.ID == inputId select new { p.FirstName, p.LastName }; return query ; }

LINQ to SQL (we’re going to need to take a trip to VisualStudio 2008 for this)

Custom LINQ Providers LINQ to Amazon LINQ to Google LINQ to Google Desktop LINQ to Flickr

LINQ to Amazon public IEnumerable<AmazonBook> SelectBooks() { var query = from book in new Amazon.BookSearch() where ( book.Title.Contains(“Spider-Man") && (book.Publisher == “Lee") && (book.Price <= 25) && (book.Condition == BookCondition.New) ) select book; return query ; }

Summary Overview of LINQ Language changes to facilitate LINQ Extension methods Lambda Expressions Anonymous constructors Anonymous fields Anonymous types and implicit typing LINQ Providers LINQ to Objects LINQ to XML LINQ to SQL

Linq And Its Impact On The.Net Framework

More Related Content

What's hot (20)

Viewers also liked (6)

Similar to Linq And Its Impact On The.Net Framework (20)

Recently uploaded (20)

Linq And Its Impact On The.Net Framework