Language Integrated Query: An introduction - … · Language Integrated Query: An introduction. What is LINQ? ... SQL LINQ to Objects LINQ to XML LINQ to Datasets LINQ to Enes LINQ

DamienGuard(BSc,MBCS)http://[email protected]

GuernseySoftwareDeveloperForumhttp://developers.org.gg

Language Integrated Query: An introduction

What is LINQ?

• LanguageIntegratedQuery

• Makequeryapartofthelanguage

• Componentof.NETFramework3.5

• NowshippingwithVisualStudio2008

Query without LINQ

• ObjectsusingloopsandcondiVonsforeach(Customer c in customers) if (c.Region == "UK") ...

• DatabasesusingSQLSELECT * FROM Customers WHERE Region='UK'

• XMLusingXPath/XQuery//Customers/Customer[@Region='UK']

ADO without LINQSqlConnection con = new SqlConnection(...);con.Open(); SqlCommand cmd = new SqlCommand( @"SELECT * FROM Customers WHERE c.Region = @Region", con );cmd.Parameters.AddWithValue("@Region", "UK"); DataReader dr = cmd.ExecuteReader(); while (dr.Read()) { string name = dr.GetString(dr.GetOrdinal("Name")); string phone = dr.GetString(dr.GetOrdinal("Phone")); DateTime date = dr.GetDateTime(3);}dr.Close();con.Close();

Query with LINQ

C#var myCustomers = from c in customers where c.Region == "UK" select c;

VB.NETDim myCustomers = From c In customers _ Where c.Region = "UK" _ Select c

More LINQ queries

C#var goodCusts = (from c in db.Customers where c.PostCode.StartsWith("GY") orderby c.Sales descending select c).Skip(10).Take(10);

VB.NETDim goodCusts = (From c In db.Customers _ Where c.PostCode.StartsWith("GY") _ Order By c.Sales Descending _ Select c).Skip(1).Take(10)

Advantages

• UnifieddataaccessSinglesyntaxtolearnandremember

• StronglytypedCatcherrorsduringcompilaVon

• IntelliSensePromptforsyntaxanda]ributes

• Bindableresultsets

ArchitectureOthersC# VB.NET

.NETLanguageIntegratedQuery(LINQ)

LINQtoSQL

LINQtoObjects

LINQtoXML

LINQtoDatasets

LINQtoEnVVes

LINQdatasourceproviders

ADO.NETsupportforLINQ

LINQ to ObjectsC#int[] nums = new int[] {0,4,2,6,3,8,3,1};double average = nums.Take(6).Average();var above = from n in nums where n > average select n;

VB.NETDim nums() As Integer = {0,4,2,6,3,8,3,1}Double average = nums.Take(6).Average()Dim above = From n In nums _ Where n > average _ Select n

LINQ to Objects

• QueryanyIEnumerable<T>sourceIncludesarrays,List<T>,DicVonary...

• ManyusefuloperatorsavailableSum,Max,Min,DisVnct,Intersect,Union

• ExposeyourowndatawithIEnumerable<T>orIQueryable<T>

• Createoperatorsusingextensionmethods

LINQ operatorsAggregate Conversion Ordering ParVVoning Sets

AggregateAverageCountMaxMinSum

CastOfTypeToArrayToDictionaryToListToLookupToSequence

OrderByThenByDescendingReverse

SkipSkipWhileTakeTakeWhile

ConcatDistinctExceptIntersectUnion

andmanyothers

LINQ to SQL• Object‐relaVonalmapping

Recordsbecomestrongly‐typedobjects

• Datacontextisthecontrollermechanism

• Facilitatesupdate,delete&insert

• TranslatesLINQqueriesbehindthescenes

• Type,parameterandinjecVonsafe

Database mapping

• VS2008designerorSQLMetalcommand

• Maptables&fieldstoclasses&properVes

• GeneratesparValclasseswitha]ributes

• Eachrecordbecomesanobject

• Datacontextrepresentsthedatabase

• UVlisetables,viewsorstoredprocedures

Modifying objects

• UpdateSetobjectproperVes

• Deletecontext.Table.DeleteOnSubmit(object)

• Insertcontext.Table.InsertOnSubmit(object)

• Commitchangesbackcontext.SubmitChanges()

TransacVonal‐allornothing

Demo of LINQ to SQL

Additional providers

• RelaVonaldataNHibernate,MySQL,Oracle,PostgreSQL

• WebservicesRDF,Flickr,Amazon,WebQueries

• CustomLDAP,GoogleDesktop,SharePoint,TerraServermaps

Future developments

• BlinqScaffoldwebUIforlist/view/updatepages

• PLINQParallelqueryprocessingovermanyCPUs

• SyncLINQ&ConVnuousLINQUpdatedresultsviaINoVfyCollecVonChanged

Limitations

LINQ• Onlydefinesquery,notupdateorcontext

LINQToSQL• MappingissetatcompileVme• Cannotmixmappedandunmapped

properVesinasinglequery• MicrosohSQLServer2000,2005only

.NET features used

.NETFramework2.0

• ParValclasses(mapping)

.NETFramework3.5

• Anonymoustypes(shaping)

• Extensionmethods(queryoperators)

• Typeinference(varkeyword)

• Lambdaexpressions(querysyntax)

Alternatives for .NET

• NHibernate

• CastleMonoRail/AcVveRecord

• SubSonic

• CodegeneraVontool+templatesCodeSmith,MyGeneraVon,LLBLGen/Pro+NetTiers,DooDads,rollyourown...

More information

• Officialsite‐msdn.microsoh.com/linq/

• Tutorials‐weblogs.asp.net/sco]gu/

• Screencasts‐Vnyurl.com/yusch

• ThispresentaVon&cheatsheetdamieng.com/blog/tag/linq

Questions & answers