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Paul Kimmel
LINQ
U N L E A S H E D
C
#
for
800 East 96th Street,Indianapolis,Indiana 46240 USA
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LINQ Unleashed for C# Editor-in-Chief
Copyright © 2009 by Pearson Education,Inc. Karen Gettman
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Contents at a Glance
Introduction...................................................................................1
Part I Getting Ready for LINQ
1 Programming with Anonymous Types.................................................5
2 Using Compound Type Initialization.................................................29
3 Defining Extension and Partial Methods............................................61
4 yield return: Using .NET’s State Machine Generator.............................85
5 Understanding Lambda Expressions and Closures................................97
6 Using Standard Query Operators.....................................................121
Part II LINQ for Objects
7 Sorting and Grouping Queries........................................................137
8 Using Aggregate Operations...........................................................151
9 Performing Set Operations.............................................................167
10 Mastering Select and SelectMany.....................................................185
11 Joining Query Results....................................................................211
12 Querying Outlook and Active Directory...........................................239
Part III LINQ for Data
13 Querying Relational Data with LINQ...............................................265
14 Creating Better Entities and Mapping Inheritance and Aggregation.......289
15 Joining Database Tables with LINQ Queries ......................................309
16 Updating Anonymous Relational Data.............................................349
17 Introducing ADO.NET 3.0 and the Entity Framework.........................383
Part IV LINQ for XML
18 Extracting Data from XML.............................................................415
19 Comparing LINQ to XML with Other XML Technologies....................437
20 Constructing XML from Non-XML Data...........................................453
21 Emitting XML with the XmlWriter..................................................463
22 Combining XML with Other Data Models........................................469
23 LINQ to XSD Supports Typed XML Programming..............................485
Index.........................................................................................499
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Table of Contents
Introduction 1
Conventions Used in This Book.........................................................2
Part I Getting Ready for LINQ
1 Programming with Anonymous Types 5
Understanding Anonymous Types......................................................6
Programming with Anonymous Types.................................................7
Defining Simple Anonymous Types.............................................7
Using Array Initializer Syntax.....................................................7
Creating Composite Anonymous Types.......................................9
Using Anonymous Type Indexes in For Statements......................12
Anonymous Types and Using Statements...................................14
Returning Anonymous Types from Functions..............................17
Databinding Anonymous Types........................................................18
Testing Anonymous Type Equality....................................................23
Using Anonymous Types with LINQ Queries......................................24
Introducing Generic Anonymous Methods.........................................25
Using Anonymous Generic Methods..........................................26
Implementing Nested Recursion...............................................27
Summary......................................................................................28
2 Using Compound Type Initialization 29
Initializing Objects with Named Types...............................................30
Implementing Classes for Compound Initialization Through
Named Types.......................................................................32
Understanding Auto-Implemented Properties..............................34
Initializing Anonymous Types..........................................................34
Initializing Collections....................................................................36
Finishing the Hypergraph........................................................39
Implementing the Hypergraph Controls Using the Observer
Pattern...............................................................................47
Using Conversion Operators............................................................51
ToArray................................................................................51
OfType.................................................................................54
Cast.....................................................................................54
AsEnumerable........................................................................55
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Contents v
ToList...................................................................................56
ToDictionary.........................................................................57
ToLookup..............................................................................58
Summary......................................................................................60
3 Defining Extension and Partial Methods 61
Extension Methods and Rules of the Road..........................................61
Defining Extension Methods............................................................64
Implementing Extension Methods............................................64
Overloading Extension Methods...............................................67
Defining Generic Extension Methods.........................................69
How Extension Methods Support LINQ.............................................73
Implementing a “Talking” String Extension Method............................78
Defining Partial Methods.................................................................79
Summary......................................................................................84
4 yield return: Using .NET’s State Machine Generator 85
Understanding How yield return Works.............................................86
Using yield return and yield break....................................................88
Profiling Code.......................................................................93
Using yield break...................................................................95
Summary......................................................................................95
5 Understanding Lambda Expressions and Closures 97
Understanding the Evolution from Function Pointers to Lambda
Expressions.................................................................................98
Writing Basic Lambda Expressions...................................................101
Automatic Properties.............................................................102
Reading Lambda Expressions..................................................103
Lambda Expressions Captured as Generic Actions......................104
Searching Strings..................................................................106
Lambda Expressions Captured as Generic Predicates...................108
Binding Control Events to Lambda Expressions.........................109
Dynamic Programming with Lambda Expressions..............................110
Using Select<T> with Lambda Expressions................................110
Using Where<T> with Lambda Expressions...............................112
Using OrderBy<T> with Lambda Expressions.............................113
Compiling Lambda Expressions as Code or Data........................114
Lambda Expressions and Closures...................................................117
Currying.....................................................................................119
Summary....................................................................................120
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vi LINQ Unleashed
6 Using Standard Query Operators 121
Understanding How LINQ Is Implemented.......................................121
Constructing a LINQ Query...........................................................122
Filtering Information....................................................................122
Using Quantifiers.........................................................................124
Partitioning with Skip and Take......................................................126
Using Generation Operations.........................................................127
DefaultIfEmpty.....................................................................127
Empty.................................................................................127
Range.................................................................................127
Repeat................................................................................128
Equality Testing...........................................................................129
Obtaining Specific Elements from a Sequence...................................131
Appending Sequences with Concat..................................................132
Summary....................................................................................133
Part II LINQ for Objects
7 Sorting and Grouping Queries 137
Sorting Information......................................................................137
Sorting in Ascending and Descending Order .............................138
Sort in Descending Order Using the Extension Method Directly...140
Performing Secondary Sorts....................................................141
Reversing the Order of Items..................................................144
Grouping Information...................................................................145
Summary....................................................................................150
8 Using Aggregate Operations 151
Aggregating.................................................................................151
Averaging Collection Values...........................................................154
Counting Elements.......................................................................157
Finding Minimum and Maximum Elements......................................157
Summing Query Results ................................................................162
Median: Defining a Custom Aggregation Operation...........................163
Summary....................................................................................165
9 Performing Set Operations 167
Finding Distinct Elements..............................................................167
Finding Distinct Objects Using Object Fields.............................169
Defining Exclusive Sets with Intersect and Except..............................177
Creating Composite Resultsets with Union.......................................182
Summary....................................................................................184
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Contents vii
10 Mastering Select and SelectMany 185
Exploring Select...........................................................................185
Selecting with Function Call Effects.........................................186
Manipulating Select Predicates................................................190
Returning Custom Business Objects from a Data Access Layer......190
Using Select Indexes to Shuffle (or Unsort) an Array...................194
Forming the Basis of a Card Game Like Blackjack.......................195
Projecting New Types from Calculated Values............................200
Importing DLLs....................................................................200
Using GDI+ with Windows API (or External DLL) Methods..........201
Using Select to I-Cap Words...................................................201
Projecting New Types from Multiple Sources.....................................203
Creating a New Sequence from Multiple Sequences with SelectMany....205
Using SelectMany with Indexes......................................................207
Summary....................................................................................209
11 Joining Query Results 211
Using Multiple From Clauses..........................................................211
Defining Inner Joins.....................................................................213
Using Custom, or Nonequijoins......................................................214
Defining a Nonequal Custom Join...........................................215
Defining a Custom Join with Multiple Predicates.......................219
Defining Custom Joins with a Temporary Range Variable............220
Implementing Group Join and Left Outer Join..................................224
Defining a Group Join...........................................................224
Implementing a Left Outer Join..............................................226
Implementing a Cross Join.............................................................228
Defining Joins Based on Composite Keys..........................................237
Summary....................................................................................237
12 Querying Outlook and Active Directory 239
LINQ to Outlook..........................................................................239
Querying Active Directory with Straight C# Code..............................243
LINQ to Active Directory...............................................................245
Creating an IQueryable LINQ Provider.....................................245
Implementing the IQueryProvider...........................................246
Defining Active Directory as the Data Source.............................248
Converting a LINQ Query to an Active Directory Query..............252
Implementing Helper Attributes..............................................257
Defining Active Directory Schema Entities................................259
Querying Active Directory with LINQ..............................................260
Summary....................................................................................262
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viii LINQ Unleashed
Part III LINQ for Data
13 Querying Relational Data with LINQ 265
Defining Table Objects..................................................................266
Mapping Classes to Tables......................................................269
Viewing the Query Text Generated by LINQ..............................273
Connecting to Relational Data with DataContext Objects...................275
Querying DataSets........................................................................277
Selecting Data from a DataTable..............................................278
Querying the DataTable with a Where Clause............................280
Using Partitioning Methods....................................................282
Sorting Against DataTables.....................................................282
Defining a Join with DataSets.................................................282
SqlMetal: Using the Entity Class Generator Tool................................285
Using the LINQ to SQL Class Designer.............................................285
Summary....................................................................................287
14 Creating Better Entities and Mapping Inheritance and Aggregation 289
Defining Better Entities with Nullable Types.....................................289
Mapping Inheritance Hierarchies for LINQ to SQL.............................294
Creating Inheritance Mappings with the LINQ to SQL Designer...298
Customizing Classes Created with the LINQ to SQL Designer.......299
Adding EntitySet Classes as Properties..............................................300
Creating Databases with LINQ to SQL..............................................305
Summary....................................................................................308
15 Joining Database Tables with LINQ Queries 309
Defining Joins with LINQ to DataSet...............................................310
Coding Equijoins..................................................................310
Coding Nonequijoins............................................................312
Defining a Left Join and a Word about Right Joins.....................313
Considering Right Joins.........................................................315
Defining Joins with LINQ to SQL....................................................317
Coding Equijoins..................................................................317
Implementing the Group Join.................................................321
Implementing a Left Join.......................................................331
Querying Views with LINQ............................................................340
Building a View in SQL Server.................................................340
Querying a View with LINQ to SQL.........................................342
Databinding with LINQ to SQL.......................................................345
Summary....................................................................................347
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Contents ix
16 Updating Anonymous Relational Data 349
Adding and Removing Data...........................................................349
Inserting Data with LINQ to SQL.............................................349
Deleting Data with LINQ to SQL.............................................352
Updating Data with LINQ to SQL............................................354
Using Stored Procedures.........................................................355
Calling User-Defined Functions......................................................363
Using Transactions.......................................................................366
Understanding Conflict Resolution..................................................368
Indicating the Conflict Handling Mode for SubmitChanges.........369
Catching and Resolving Concurrency Conflicts.........................371
N-Tier Applications and LINQ to SQL..............................................376
Summary....................................................................................382
17 Introducing ADO.NET 3.0 and the Entity Framework 383
Understanding the General Nature of the Problem and the Solution.....384
Understanding Problems with the Relational Database
Model as It Pertains to C# Programmers.................................384
Understanding How the Entity Framework Is Designed to Help....385
Grokking the Nature of the Solution........................................385
Finding Additional Resources.........................................................386
Wikipedia............................................................................387
Entity SQL Blog....................................................................387
Downloading and Installing the Entity Framework.....................387
Downloading Samples...........................................................388
Go Live Estimate..................................................................388
Building a Sample Application Using Vanilla ADO.NET Programming...389
Defining a Database for Storing Stock Quotes............................389
Adding a Stored Procedure for Inserting Quotes.........................390
Adding a Foreign Key............................................................393
Reference: The Complete Sample Database Script.......................394
Writing Code to Obtain the Stock Quotes and Update
the Database......................................................................397
Programming with the Entity Framework.........................................401
Creating the Entity Data Model ..............................................401
Adding an Association...........................................................402
Querying the Entity Data Model with Entity SQL.......................402
Querying the Entity Data Model with LINQ to Entities...............405
Doing It All with LINQ..................................................................406
Summary....................................................................................411
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