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Pro LINQ

Language Integrated Query in C#

2010

Adam Freeman and Joseph C. Rattz, Jr.

Apress

Contents

Contents at a Glance IV

Contents vi

About the Author xx

About the Technical Reviewer xxi

Acknowledgments xxii

Part 1: Pro LINQ: Language Integrated Query in C# 2010 1

Chapter 1: Hello LINQ 3

A Paradigm Shift 3

Query XML 4

Query a SQL Server Database 5

Introduction 7

LINQ Is About Data Queries 7

How to Obtain LINQ 8

LINQ Is Not Just for Queries 8

Tips to Get You Started 12

Use the var Keyword When Confused 12

Use the Cast or OfType Operators for Legacy Collections 14

The OfType Operator versus the Cast Operator 15

Don't Assume a Query Is Bug-Free 15

Take Advantage of Deferred Queries 16

Use the DataContext Log 17

Use the LINQ Forum 18

Summary 18

vi

CONTENTS

Chapter 2: C# Language Enhancements for LINQ 21

C# Language Additions 21

Lambda Expressions 22

Expression Trees 27

Keyword var, Object Initialization, and Anonymous Types 28

Extension Methods 33

Partial Methods 39

Query Expressions 41

Summary 52

Part 2: LINQ to Objects 55

Chapter 3: LINQ to Objects Introduction 57

LINQ to Objects Overview 57

IEnumerable<T>, Sequences, and the Standard Query Operators 58

Returning IEnumerable<T>, Yielding, and Deferred Queries 59

Func Delegates 62

The Standard Query Operators Alphabetical Cross-Reference 64

A Tale of Two Syntaxes 66

Summary 66

Chapter 4: Deferred Operators 69

Referenced Namespaces 69

Referenced Assemblies 69

Common Classes 69

The Deferred Operators by Purpose 71

Restriction 71

Projection 74

Partitioning 85

Concatenation 93

Ordering 96

Join 116

vii

CONTENTS

Grouping

Set 126

Conversion 133

Element 140

Generation 145

Summary 148

Chapter 5: Nondeferred Operators 151


Common Classes 151

The Nondeferred Operators by Purpose 154

Conversion 155

Equality 168

Element 172

Quantifiers 187

Aggregate 193

Summary 209

Part 3: LINQ to XML 211

Chapter 6: LINQ to XML Introduction 213

Introduction 215

Cheating the W3C DOM XML API 216

Summary 217

Chapter 7: The LINQ to XML API 219


Significant API Design Enhancements 219

XML Tree Construction Simplified with Functional Construction 220

Document Centricity Eliminated in Favor of Element Centricity 222

Names, Namespaces, and Prefixes 224

Node Value Extraction 227

The LINQ to XML Object Model 230

CONTENTS

Deferred Query Execution, Node Removal, and the Halloween Problem 231

XML Creation 234

Creating Elements with XEIement 234

Creating Attributes with XAttribute 237

Creating Comments with XComment 238

Creating Containers with XContainer 238

Creating Declarations with XDeclaration 239

Creating Document Types with XDocumentType 240

Creating Documents with XDocument 241

Creating Names with XName 242

Creating Namespaces with XNamespace 243

Creating Nodes with XNode 243

Creating Processing Instructions with XProcessinglnstruction 243

Creating Streaming Elements with XStreamingElement 246

Creating Text with XText 247

Creating CData with XCData 248

XML Output 248

Saving with XDocument.Save() 248

Saving with XEIement.Save() 250

XML Input 251

Loading with XDocument.Load() 251

Loading with XEIement.Load() 253

Parsing with XDocument.Parse() or XEIement.Parse() 254

XML Traversal 254

Traversal Properties 255

Traversal Methods 260

XML Modification 276

Adding Nodes 276

Deleting Nodes 281

Updating Nodes 284

ix

CONTENTS

XEIement.SetElementValue() on Child XEIement Objects 289

XML Attributes •290

Attribute Creation 291

Attribute Traversal • 291

Attribute Modification 295

XML Annotations 300

Adding Annotations with XObject.AddAnnotation() 300

Accessing Annotations with XObject.Annotation() or XObject.Annotations() 300

Removing Annotations with XObject.RemoveAnnotations() 301

Annotations Example 301

XML Events 304

XObjectChanging 305

XObjectChanged 305

A Couple of Event Examples 306

Trick or Treat, or Undefined? 310

Summary 310

Chapter 8: LINQ to XML Operators 313

Introduction to LINQ to XML Operators 313

Ancestors 314

Prototypes 314

Examples 314

AncestorsAndSelf 319

Prototypes 319

Examples 319

Attributes 322

Prototypes 322

Examples 322

DescendantNodes 324

Prototypes 324

Examples 325

CONTENTS

DescendantNodesAndSelf 326

Prototypes 326

Examples 327

Descendants 328

Prototypes 328

Examples 329

DescendantsAndSelf 331

Prototypes 331

Examples 331

Elements 334

Prototypes 334

Examples 334

InDocumentOrder 336

Prototypes 337

Examples 337

Nodes 338

Prototypes 338

Examples 339

Remove .340

Prototypes 340

Examples 340

Summary 343

Chapter 9: Additional XML Capabilities 345

Referenced Namespaces ,

345

Queries 346

No Reaching 346

A Complex Query 348

Transformations 355

Transformations Using XSLT 355

Transformations Using Functional Construction 357

CONTENTS

Tips359

Validation... 366

The Extension Methods 366

Prototypes367

Obtaining an XML Schema 368

Examples 370

XPath •383

Prototypes 383

Examples 384

Summary 384

Part 4: LINQ to DataSet.. 387

Chapter 10: LINQ to DataSet Operators 389

Assembly References 390


Common Code for the Examples 390

DataRow Set Operators 392

Distinct 392

Except 396

Intersect 399

Union 401

SequenceEqual 403

DataRow Field Operators 405

Field<T> 410

SetField<T> 415

DataTable Operators 419

AsEnumerable 419

CopyToDataTable<DataRow> 419

Summary 425

Chapter 11: Additional DataSet Capabilities 427

Required Namespaces,

427

xii

CONTENTS

Typed DataSets 427

Putting It All Together 429

Summary 432

Part 5: LINQ to SQL 435

Chapter 12: LINQ to SQL Introduction . 437

Introducing LINQ to SQL 438

The DataContext 439

Entity Classes 440

Associations 440

Concurrency Conflict Detection 441

Concurrency Conflict Resolution 441

Prerequisites for Running the Examples 442

Obtaining the Appropriate Version of the Northwind Database 442

Generating the Northwind Entity Classes 442

Generating the Northwind XML Mapping File 444

Using the LINQ to SQL API 444

IQueryable<T> 444

Some Common Methods 444

GetStringFromDb() 445

ExecuteStatementlnDbO 446

Summary 447

Chapter 13: LINQ to SQL Tips and Tools 449

Introduction to LINQ to SQL Tips and Tools 449

Tips 449

Use the DataContextlog Property 450

Use the GetChangeSet() Method 451

Consider Using Partial Classes or Mapping Files 451

Consider Using Partial Methods 451

Tools 452

SQLMetal 452

xiii

CONTENTS

The Object Relational Designer 41)0

Use SQLMetal and the O/R Designer Together 472

Summary -473

Chapter 14: LINQ to SQL Database Operations 475




Standard Database Operations 476

Inserts 4?6

Queries 480

Updates 506

Deletes 510

Overriding Database Modification Statements 513

Overriding the Insert Method 513

Overriding the Update Method 514

Overriding the Delete Method 514

Example 514

Overriding in the Object Relational Designer 517

Considerations 517

SQL Translation 517

Summary 520

Chapter 15: LINQ to SQL Entity Classes 521


Entity Classes 521

Creating Entity Classes 521

XML External Mapping File Schema 552

Projecting into Entity Classes vs. Nonentity Classes 552

Extending Entity Classes with Partial Methods 558

Important System.Data.Linq API Classes 560

xiv

CONTENTS

EntitySet<T> 560

EntityRef<T> 560

Table<T> 563

lExecuteResult 564

ISingleResult<T> 565

IMultipleResults 565

Summary 567

Chapter 16: The LINQ to SQL DataContext 569




[Your]DataContext Class 569

The DataContext Class 570

The DataContext Class Implements IDisposable 573

Primary Purposes 573

The Data Context Lifetime 580

DataContext() and [Your]DataContext() 580

SubmitChangesO 594

DatabaseExists() 602

CreateDatabase() 603

DeleteDatabase() 604

CreateMethodCallQuery() 605

ExecuteQuery() 607

Translate!) 610

ExecuteCommandO 612

ExecuteMethodCall() 613

GetCommand() 621

GetChangeSetO 623

GetTable() 625

RefreshO 626

Summary 634

XV

CONTENTS

Chapter 17: LINQ to SQL Concurrency Conflicts.... 635




Concurrency Conflicts 635

Optimistic Concurrency 636

Pessimistic Concurrency 647

An Alternative Approach for Middle Tiers and Servers 650

Summary - 652

Chapter 18: Additional UNQ to SQL Capabilities 653



Using the LINQ to XML API 653

Database Views 653

Entity Class Inheritance 655

Transactions 661

Summary 663

Part 6: LINQ to Entities 665

Chapter 19: LINQ to Entities Introduction 667

Introducing LINQ to Entities 668

The ObjectContext 669

Entity Classes 669

Associations 670


Obtaining the Appropriate Version of the Northwind Database 670

Generating the Northwind Entity Data Model 670

Using the LINQ to Entities API 674

IQueryable<T> 674

Some Common Methods,

675

xvi

CONTENTS

GetStringFromDb() 675

ExecuteStatementlnDb() 676

Summary 677

Chapter 20: LINQ to Entities Operations .679



Standard Database Operations 680

Inserts 680

Queries 687

Updates 704

Deletes ...705

Managing Concurrency 715

Enabling Concurrency Checks 716

Handling Concurrency Conflicts 717

Summary 722

Chapter 21: LINQ to Entities Classes 723


The ObjectContext Class 723

Constructor 724

DatabaseExists() 726

DeleteDatabase() 726

CreateDatabase() 727

SaveChanges() 727

RefreshO 728

AddObject() 729

CreateObject() 730

DeleteObject() 731

EntityObject 732

Constructor 732

Factory Method 733

xvii

CONTENTS

Primitive Properties 735

Navigation Properties 737

EntityReference 740

Load() 740

Value 741

EntityCollection 741

AddO 741

Remove() 743

ClearO 745

ContainsO 745

Load() 747

Count 747

Summary 748

Part 7: Parallel LINQ 749

Chapter 22: Parallel LINQ Introduction 751

Introducing Parallel LINQ 751

Parallel LINQ Is for Objects 756

Using the LINQ to Entities API 756

Summary 756

Chapter 23: Using Parallel LINQ 757

Creating a Parallel LINQ Query 757

Preserving Result Ordering 760

Controlling Parallelism 763

Forcing Parallel Execution 763

Limiting the Degree of Parallelism 764

Dealing with Exceptions 764

Queries Without Results 768

Creating Ranges and Repetitions 770

Summary 771

xviii

CONTENTS

Chapter 24: Parallel LINQ Operators .773

ParallelQuery Creation Operators 773

AsParallel 773

Range 777

Repeat 778

Empty 779

Execution Control Operators 779

AsOrdered 779

AsUnordered 782

AsSequential 783

AsEnumerable 784

WithDegreeOfParallelism 785

WithExecutionMode 786

WithMergeOptions 787

Conversion Operators 790

Cast 790

OtType 791

The ForAII Operator 792

Prototypes 792

Examples 792

Summary 793

Index 795

xix