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LINQ

16/10/2008

Agenda

• Impedance Mismatch• C# 3.0 New Features• Introduction to LINQ• LINQ to Objects• LINQ to SQL• LINQ to XML• Summary

Impedance Mismatch•Incompatibility between systems.

•Describes an inadequate ability of one system to accommodate input from another.

Introduction

RDBMS

Business Logic

Windows UI

Web UIConsole

Web Service

Windows Service

Impedance MismatchData Access

C# 3.0 Features

• Implicitly Typed Local Variables• Automatic Properties• Object and Collection Initializers• Anonymous Types• Extension Methods• Lambda Expressions• LINQ

Implicitly Typed Local Variables

• The var keyword

// C# 2.0int x = 5;string name = "Bart Simpson";Dictionary<string, object> data = new Dictionary<string, object>();int size = name.Length;

// C# 3.0var x = 5;var name = "Bart Simpson";var data = new Dictionary<string, object>();var size = name.Length;

var y = x;var keys = data.Keys; // Dictionary<string, object>.KeyCollection

Automatic Propertiespublic class Person { // C# 2.0

private string _firstName, _lastName;

private int _age;

public string FirstName {get { return _firstName; }set { _firstName = value; }

}public string LastName {

get { return _lastName; }set { _lastName = value; }

}public int Age {

get { return _age; }set { _age = value; }

}}

public class Person { // C# 3.0public string FirstName { get;

set; }public string LastName { get; set; }public int Age { get; set; }

}

Object Initializers// C# 2.0

Person p = new Person();p.FirstName = "Bart";p.LastName = "Simpson";p.Age = 12;

// C# 3.0

Person p = new Person() { FirstName = "Bart", LastName = "Simpson", Age = 12

};

Collection Initializers// C# 3.0

List<Person> people = new List<Person>();people.Add(new Person() {

FirstName = "Bart", LastName = "Simpson", Age = 12 });people.Add(new Person() {

FirstName = "Clark", LastName = "Kent", Age = 35 });people.Add(new Person() {

FirstName = "Peter", LastName = "Parker", Age = 30 });// C# 3.0

var people = new List<Person>() {new Person() { FirstName = "Bart", LastName = "Simpson", Age =

12 },new Person() { FirstName = "Clark", LastName = "Kent", Age =

35 },new Person() { FirstName = "Peter", LastName = "Parker", Age =

30 }};

Anonymous Types

var people = new[] {new { FirstName = "Clark", LastName = "Kent", Age = 36 },new { FirstName = "Peter", LastName = "parker", Age = 26 },new { FirstName = "Bart", LastName = "Simpson", Age = 11 }

};

foreach (var i in people)Console.WriteLine("{0} {1} ({2})", i.FirstName, i.LastName,

i.Age);

Console.WriteLine(people[0].GetType().FullName); // ???

In which the type name is generated by the compiler andIs not available at the source code level.

Extension Methods

•Extension methods allows us to “add” method to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.

•Extension methods are a special kind of “static” method, but they are called as if they were instance methods.

•The first parameter specifies which type the method operates on, and the parameter is preceded by the “this” modifier.

Extension Methods

public static class MyExtensions {public static string UpperLower(this string str, bool

upperFirst) {StringBuilder newString = new StringBuilder(str.Length);for (int i = 0; i < str.Length; i++) {

newString.Append(upperFirst ? char.ToUpper(str[i]) :char.ToLower(str[i]));

upperFirst = !upperFirst; } return newString.ToString(); }}

string input = Console.ReadLine();Console.WriteLine("calling extension method for {0}: {1}", input,

input.UpperLower(true));

Lambda Expressions

A lambda expression is an anonymous function that can contain expressions and statements, and can be used to create delegates or expression tree types.

var x => x+1; //Implicitly typed expression.

var x => { return x+1;} //Implicitly type statement.

int x => x+1; //Explicitly typed expression.

int x => {return x+1;} //Explicitly type statement.

var prs = Process.GetProcesses() .Where(process => process.WorkingSet64 > 20 * 1024 * 1024) .OrderByDescending(process => process.WorkingSet64) .Select(process => new { process.Id, Name = process.ProcessName });

Extension Extension methodsmethods

Local Local variable type variable type

inferenceinference

Anonymous Anonymous typestypes

Object Object initializersinitializers

Lambda Lambda expressionsexpressions

Language Extensions

Introduction to LINQ• What is LINQ?

• Stands for Language INtegrated Query• Allows developers to query data structures using

SQL-like syntax from within their application’s code• Is available to both C# and Visual Basic developers

in Visual Studio 2008

The LINQ ProjectC# 3.0C# 3.0 Visual Visual

Basic 9.0Basic 9.0 OthersOthers

.NET Language Integrated Query.NET Language Integrated Query

LINQ to ObjectsC# 3.0C# 3.0 Visual Visual

Basic 9.0Basic 9.0 OthersOthers

.NET Language Integrated Query.NET Language Integrated Query

LINQ to Object example• LINQ Example - Querying an array

//Create an array of integersint[] myarray = new int[] { 49, 28, 20, 15, 25, 23, 24, 10, 7, 34 };

//Create a query for odd numbersvar oddNumbers = from i in myarray where i % 2 == 1 select i;

//Display the results of the queryforeach (int i in oddNumbers) Console.WriteLine(i);

//Create a query for odd numbers, sortedvar oddNumbers = from i in myarray where i % 2 == 1 orderby i select i;

//Create a query for odd numbers, sorted in descending ordervar oddNumbers = from i in myarray where i % 2 == 1 orderby i descending select i;

//Create a query for odd numbersvar oddNumbers = from i in myarray where i % 2 == 1 select i;

//Compose the original query to create a query for odd numbersvar sorted = from i in oddNumbers orderby i descending select i;

using System;using System.Query;using System.Collections.Generic; class app { static void Main() { string[] names = { "Allen", "Arthur",

"Bennett" };  IEnumerable<string> ayes = names

.Where(s => s[0] == 'A');  foreach (string item in ayes)

Console.WriteLine(item);  names[0] = "Bob";  foreach (string item in ayes)

Console.WriteLine(item); }}

Arthur

LINQ to Objects• Native query syntax

in C# and VB– IntelliSense– Autocompletion

• Query Operators can be used against any .NET collection (IEnumerable<T>)

– Select, Where, GroupBy, Join, etc.

• Deferred Query Evaluation

• Lambda Expressions

using System;using System.Query;using System.Collections.Generic; class app { static void Main() { string[] names = { "Allen", "Arthur",

"Bennett" };  IEnumerable<string> ayes = names

.Where(s => s[0] == 'A');  foreach (string item in ayes)

Console.WriteLine(item);  names[0] = "Bob";  foreach (string item in ayes)

Console.WriteLine(item); }}

AllenArthur

using System;using System.Query;using System.Collections.Generic; class app { static void Main() { string[] names = { "Burke", "Connor",

"Frank", "Everett", "Albert", "George",

"Harris", "David" };  IEnumerable<string> expr =

from s in names where s.Length == 5 orderby s select s.ToUpper();  foreach (string item in expr) Console.WriteLine(item); }}

BURKEDAVIDFRANK

using System;using System.Query;using System.Collections.Generic; class app { static void Main() { string[] names = { "Burke", "Connor",

"Frank", "Everett", "Albert", "George",

"Harris", "David" };  Func<string, bool> filter = s => s.Length == 5; Func<string, string> extract = s => s; Func<string, string> project = s = s.ToUpper();  IEnumerable<string> expr = names

.Where(filter)

.OrderBy(extract) .Select(project);  foreach (string item in expr) Console.WriteLine(item); }}

BURKEDAVIDFRANK

LINQ to SQLC# 3.0C# 3.0 Visual Visual

Basic 9.0Basic 9.0 OthersOthers

.NET Language Integrated Query.NET Language Integrated Query

LINQ to SQL Architecture

ApplicationApplication

LINQ to SQLLINQ to SQL

from c in db.Customerswhere c.City == "London"select c.CompanyName

EnumeratEnumeratee

SELECT CompanyNameFROM CustomerWHERE City = 'London'

SQL QuerySQL Queryor SProcor SProc

RowsRows

ObjectsObjects

db.Customers.Add(c1);c2.City = “Seattle";db.Customers.Remove(c3);

SubmitChanges()SubmitChanges()

INSERT INTO Customer …UPDATE Customer …DELETE FROM Customer …

DML DML or SProcsor SProcs

Querying SQL

SqlConnection c = new SqlConnection(…);SqlConnection c = new SqlConnection(…);c.Open();c.Open();SqlCommand cmd = new SqlCommand(SqlCommand cmd = new SqlCommand( @"SELECT c.Name, c.Phone@"SELECT c.Name, c.Phone FROM Customers cFROM Customers c WHERE c.City = @p0");WHERE c.City = @p0");cmd.Parameters["@p0"] = "London";cmd.Parameters["@p0"] = "London";DataReader dr = c.Execute(cmd);DataReader dr = c.Execute(cmd);while (dr.Read()) {while (dr.Read()) { string name = r.GetString(0);string name = r.GetString(0); string phone = r.GetString(1);string phone = r.GetString(1); DateTime date = r.GetDateTime(2);DateTime date = r.GetDateTime(2);}}r.Close();r.Close();

Accessing Accessing relational relational data todaydata today

Queries in Queries in quotesquotes

Loosely Loosely bound bound

argumentsarguments

Loosely Loosely typed result typed result

setssets

No compile No compile time checkstime checks

public class Customer { … }public class Customer { … }

public class Northwind: DataContextpublic class Northwind: DataContext{{ public Table<Customer> Customers;public Table<Customer> Customers; … …}}

Northwind db = new Northwind(…);Northwind db = new Northwind(…);var contacts =var contacts = from c in db.Customersfrom c in db.Customers where c.City == "London"where c.City == "London" select new { c.Name, c.Phone };select new { c.Name, c.Phone };

LINQ to SQLAccessing relational data with LINQAccessing relational data with LINQ

Classes Classes describe datadescribe data

Strongly Strongly typed typed

connectionconnection

Integrated Integrated query syntaxquery syntax

Strongly Strongly typed resultstyped results

Tables are Tables are like like

collectionscollections

Language Extensionsvar contacts = from c in dc.GetTable<customers>() where c.State == "WA" select new { c.Name, c.Phone };

var contacts = customers .Where(c => c.State == "WA") .Select(c => new { c.Name, c.Phone });

Extension Extension methodsmethods

Lambda Lambda expressionsexpressions

Query Query expressionsexpressions

Object Object initializersinitializers

Anonymous Anonymous typestypes

Local Local variable type variable type

inferenceinference

LINQ to XMLC# 3.0C# 3.0 Visual Visual

Basic 9.0Basic 9.0 OthersOthers

.NET Language Integrated Query.NET Language Integrated Query

LINQ to XML

• Large Improvement Over Existing Model• Declarative Model• Supports:

– Creating XML– Loading & querying XML– Modifying & saving XML

LINQ to XML

XmlDocument doc = new XmlDocument();XmlDocument doc = new XmlDocument();XmlElement contacts = doc.CreateElement("contacts");XmlElement contacts = doc.CreateElement("contacts");foreach (Customer c in customers)foreach (Customer c in customers) if (c.Country == "USA") {if (c.Country == "USA") { XmlElement e = doc.CreateElement("contact");XmlElement e = doc.CreateElement("contact"); XmlElement name = doc.CreateElement("name");XmlElement name = doc.CreateElement("name"); name.InnerText = c.CompanyName;name.InnerText = c.CompanyName; e.AppendChild(name);e.AppendChild(name); XmlElement phone = doc.CreateElement("phone");XmlElement phone = doc.CreateElement("phone"); phone.InnerText = c.Phone;phone.InnerText = c.Phone; e.AppendChild(phone);e.AppendChild(phone); contacts.AppendChild(e);contacts.AppendChild(e); }}doc.AppendChild(contacts);doc.AppendChild(contacts);

Programming XML today

<contacts><contacts> <contact><contact> <name>Great Lakes <name>Great Lakes Food</name>Food</name> <phone>(503) <phone>(503) 555-7123</phone>555-7123</phone> </contact></contact> … …</contacts></contacts>

Imperative Imperative modelmodel

Document Document centriccentric

No integrated No integrated queriesqueries

Memory Memory intensiveintensive

LINQ to XML

XElement contacts = new XElement("contacts",XElement contacts = new XElement("contacts", from c in customersfrom c in customers where c.Country == "USA"where c.Country == "USA" select new XElement("contact",select new XElement("contact", new XElement("name", c.CompanyName),new XElement("name", c.CompanyName), new XElement("phone", c.Phone)new XElement("phone", c.Phone) ))););

Programming XML with LINQDeclarative Declarative

modelmodel

ElementElementcentriccentric

Integrated Integrated queriesqueries

Smaller and Smaller and fasterfaster

Summary• LINQ will be a really important technology.

• Native query integration within languages improves productivity and error checking.

• Using LINQ with ASP.NET is both easy and fun.

• ASP.Net + LINQ - a simple and powerful way to build data driven web applications.

THANK YOU