C# in Depth

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Joins30111.5.2 Group joins with join … into clausesWe’ve seen that the result sequence from a normal join clause consistsof pairs of elements, one from each of the input sequences. A group joinlooks similar in terms of the query expression but has a significantly differentoutcome. Each element of a group join result consists of an elementfrom the left sequence (using its original range variable), and alsoa sequence of all the matching elements of the right sequence, exposed asa new range variable specified by the identifier coming after into in thejoin clause.Let’s change our previous example to use a group join. Listing 11.13 again shows allthe defects and the notifications required for each one, but breaks them out in a perdefectmanner. Pay particular attention to how we’re displaying the results, and to thenested foreach loop.ResultcontainsembeddedsubsequencesListing 11.13Joining defects and subscriptions with a group joinvar query = from defect in SampleData.AllDefectsjoin subscription in SampleData.AllSubscriptionson defect.Project equals subscription.Projectinto groupedSubscriptionsselect new { Defect=defect,Subscriptions=groupedSubscriptions };foreach (var entry in query){Console.WriteLine(entry.Defect.Summary);foreach (var subscription in entry.Subscriptions){Console.WriteLine (" {0}", subscription.EmailAddress);}}The Subscriptions property of each entry is the embedded sequence of subscriptionsmatching that entry’s defect. Figure 11.7 shows how the two initial sequences arecombined.One important difference between an inner join and a group join—and indeedbetween a group join and normal grouping—is that for a group join there’s a one-toonecorrespondence between the left sequence and the result sequence, even if someof the elements in the left sequence don’t match any elements of the right sequence.This can be very important, and is sometimes used to simulate a left outer join fromSQL. The embedded sequence is empty when the left element doesn’t match any rightelements. As with an inner join, a group join buffers the right sequence but streamsthe left one.Listing 11.14 shows an example of this, counting the number of bugs created oneach day in August. It uses a DateTimeRange (as described in chapter 6) as the leftsequence, and a projection that calls Count on the embedded sequence in the resultof the group join.Licensed to Rhona Hadida
302 CHAPTER 11 Query expressions and LINQ to Objectsfrom defect inSampleData.AllDefectsDefect: { ID=1, Project=Media player, ... }Defect: { ID=2, Project=Media player, ...}Defect: { ID=3, Project=Talk, ...}...join subscription inSampleData.AllSubscriptionson defect.Project equals subscription.Projectinto groupedSubscriptionsfrom subscription inSampleData.AllSubscriptions(NotificationSubscription sequence){ defect=Defect: { ID=1, Project=Media player ... },groupedSubscriptions= { Media player, "media-bugs@..." ... }{ Media player, "theboss@..." ...}{ defect=Defect: { ID=2, Project=Media player ... },groupedSubscriptions= { Media player, "media-bugs@..." ... }{ Media player, "theboss@..." ...}{ defect=Defect: { ID=3, Project=Talk ... },groupedSubscriptions= { Talk, "talk-bugs@..." ... }...select new { Defect=defect,Subscriptions=groupedSubscriptions }(Result of query){ Defect=Defect: { ID=1, Project=Media player ... },Subscriptions= { Media player, "media-bugs@..." ... }{ Media player, "theboss@..." ...}{ Defect=Defect: { ID=2, Project=Media player ... },Subscriptions= { Media player, "media-bugs@..." ... }{ Media player, "theboss@..." ...}{ Defect=Defect: { ID=3, Project=Talk ... },Subscriptions= { Talk, "talk-bugs@..." ... }...Figure 11.7 Sequences involved in the group join from listing 11.13. The short arrowsindicate embedded sequences within the result entries. In the output, some entriescontain multiple email addresses for the same bug.Listing 11.14Counting the number of bugs raised on each day in Augustvar dates = new DateTimeRange(SampleData.Start, SampleData.End);var query = from date in datesjoin defect in SampleData.AllDefectson date equals defect.Created.Dateinto joinedselect new { Date=date, Count=joined.Count() };Licensed to Rhona Hadida
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C# in DepthLicensed to Rhona Hadida
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C# in DepthJON SKEETMANNINGGreenwic
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Licensed to Rhona Hadida
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Licensed to Rhona Hadida
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xCONTENTS1.3 The .NET platform 24Di
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xiiCONTENTS5.4 Inline delegate acti
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xivCONTENTS9.4 Changes to type infe
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xviCONTENTS13.2 Delegation as the n
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xviiiFOREWORDOf the latter kind, th
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xxPREFACEdidn’t start using C#2 u
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xxiiACKNOWLEDGMENTSThe aforemention
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xxivABOUT THIS BOOKwant to become e
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xxviABOUT THIS BOOKSQL statements.
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about the cover illustrationThe cap
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xxxCOMMENTS FROM THE TECH REVIEWThi
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Chapter 1 presents a bird’s-eye v
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4 CHAPTER 1 The changing face of C#
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10 CHAPTER 1 The changing face of C
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Core foundations:building on C# 1Th
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34 CHAPTER 2 Core foundations: buil
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C# 2 and 3: new features on a solid
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C# 2 and 3: new features on a solid
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Summary59Listing 2.7 shows a number
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Part 2C#2:solving the issuesof C#1I
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Parameterizedtyping with genericsTh
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Simple generics for everyday use65o
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Simple generics for everyday use67I
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Simple generics for everyday use69t
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Simple generics for everyday use71N
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Simple generics for everyday use73}
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Beyond the basics75parameters. You
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Beyond the basics77NOTEC# vs. CLI s
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Beyond the basics79combined togethe
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Beyond the basics813.3.3 Implementi
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Beyond the basics83derive from a pa
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Advanced generics85implement IEquat
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Advanced generics87within another,
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Advanced generics89ArrayListobject[
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Advanced generics91}{}return new Co
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Advanced generics93Listing 3.10Usin
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Advanced generics95REFLECTING GENER
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Generic collection classes in .NET
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Limitations of generics in C# and o
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Summary111My personal opinion is th
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What do you do when you just don’
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System.Nullable and System.Nullable
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C# 2’s syntactic sugar for nullab
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Novel uses of nullable types131part
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Novel uses of nullable types133else
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Novel uses of nullable types135}{}i
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Fast-tracked delegatesThis chapter
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Saying goodbye to awkward delegate
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Covariance and contravariance141met
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Covariance and contravariance143som
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Inline delegate actions with anonym
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Capturing variables in anonymous me
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Implementingiterators the easy wayT
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C# 1: the pain of handwritten itera
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C# 2: simple iterators with yield s
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Real-life example: iterating over r
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Pseudo-synchronous code with the Co
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Summary181(without using a dedicate
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Concluding C# 2:the final featuresT
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Partial types185C# 2 allows more th
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Partial types187code generator can
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Partial types189Listing 7.2A partia
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Static classes191}public static str
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Namespace aliases193same syntax is
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Namespace aliases195Listing 7.6usin
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Pragma directives197}}Console.Write
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Fixed-size buffers in unsafe code19
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Exposing internal members to select
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Exposing internal members to select
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Part 3C# 3—revolutionizinghow we
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Cutting fluffwith a smart compilerT
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Automatically implemented propertie
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Implicit typing of local variables2
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Implicit typing of local variables2
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Simplified initialization215simple
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Simplified initialization217The par
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Simplified initialization219CREATIN
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Simplified initialization221Home =
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Implicitly typed arrays2238.4 Impli
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Anonymous types225new { Name = "Hol
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Anonymous types227That certainly wo
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Summary229typed local variables—a
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Lambda expressions and expression t
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Lambda expressions as delegates233L
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Simple examples using List and even
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Simple examples using List and even
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Expression trees239code to run on y
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Expression trees241So, what’s the
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Expression trees243the tree and how
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Changes to type inference and overl
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Page 284 and 285: Summary253find the better conversio
Page 286 and 287: Extension methodsThis chapter cover
Page 288 and 289: Life before extension methods257Sys
Page 290 and 291: Extension method syntax259extension
Page 292 and 293: Extension method syntax26110.2.3 Ho
Page 294 and 295: Extension methods in .NET 3.5263pub
Page 296 and 297: Extension methods in .NET 3.5265ret
Page 298 and 299: Extension methods in .NET 3.5267as
Page 300 and 301: Extension methods in .NET 3.5269Now
Page 302 and 303: Usage ideas and guidelines271extens
Page 304 and 305: Usage ideas and guidelines273those
Page 306 and 307: Query expressionsand LINQ to Object
Page 308 and 309: Introducing LINQ277the extension me
Page 310 and 311: Introducing LINQ279Figure 11.1 show
Page 312 and 313: Introducing LINQ281flexible. In par
Page 314 and 315: Simple beginnings: selecting elemen
Page 322 and 323: Filtering and ordering a sequence29
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Page 326 and 327: Let clauses and transparent identif
Page 328 and 329: Joins29711.5 JoinsEach part of the
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Page 338 and 339: Groupings and continuations307In ju
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Page 344 and 345: Summary31311.7 SummaryIn this chapt
Page 346 and 347: LINQ to SQL315LINQ to DataSet and L
Page 348 and 349: LINQ to SQL317■ I changed the typ
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Page 352 and 353: LINQ to SQL321FROM [dbo].[Defect] A
Page 354 and 355: LINQ to SQL323FROM [dbo].[Notificat
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Page 370 and 371: LINQ to XML339■ Create a document
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Page 374 and 375: LINQ to XML343need the string form,
Page 376 and 377: LINQ beyond .NET 3.5345Listing 12.1
Page 378 and 379: LINQ beyond .NET 3.5347LINQ TO ACTI
Page 380 and 381: LINQ beyond .NET 3.5349All of the L
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Summary351you look back at all the
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The changing nature of language pre
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Delegation as the new inheritance35
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Life in a parallel universe357Array
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appendix:LINQ standardquery operato
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Conversion361Cast and OfType conver
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Equality operations363A.4 Element o
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Joins365A.7 GroupingThere are two g
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Quantifiers367Table A.9Partitioning
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Sorting369For the examples of these
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indexSymbols!= 82with generics 76#p
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INDEX 373C# (continued)influences 1
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INDEX 375confusion 150, 222over cap
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INDEX 377Document Object Model (DOM
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INDEX 379fully qualified type name
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INDEX 381interfaces (continued)no c
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INDEX 383List`1 93lists 278local va
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INDEX 385Nullable (continued)Value
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INDEX 387RRails 22random access 102
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INDEX 389Standard Query Operators (
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INDEX 391type parameters (continued
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C# in Depth

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