Pro LINQ. Language Integrated Query in C# Apress. Adam Freeman and Joseph C. Rattz, Jr.

Transcription

1 Pro LINQ Language Integrated Query in C# 2010 Adam Freeman and Joseph C. Rattz, Jr. Apress

2 Contents Contents at a Glance Contents About the Author About the Technical Reviewer Acknowledgments Part 1: Pro LINQ: Language Integrated Query IV vi xx xxi xxii in C# 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

3 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

4 Grouping Set 126 Conversion 133 Element 140 Generation 145 Summary 148 Chapter 5: Nondeferred Operators 151 Referenced Namespaces 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 Referenced Namespaces 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

5 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

6 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

7 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

8 Tips 359 Validation The Extension Methods 366 Prototypes 367 Obtaining an XML Schema 368 Examples XPath Prototypes Examples 384 Summary 384 Part 4: LINQ to DataSet Chapter 10: LINQ to DataSet Operators 389 Assembly References 390 Referenced Namespaces 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

9 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

10 473 - The Object Relational Designer 41)0 Use SQLMetal and the O/R Designer Together 472 Summary Chapter 14: LINQ to SQL Database Operations 475 Prerequisites for Running the Examples 475 Some Common Methods 475 Using the LINQ to SQL API 476 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 Prerequisites for Running the Examples 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

11 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 Prerequisites for Running the Examples 569 Some Common Methods 569 Using the LINQ to SQL API 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

12 Chapter 17: LINQ to SQL Concurrency Conflicts Prerequisites for Running the Examples 635 Some Common Methods 635 Using the LINQ to SQL API 635 Concurrency Conflicts 635 Optimistic Concurrency 636 Pessimistic Concurrency 647 An Alternative Approach for Middle Tiers and Servers 650 Summary Chapter 18: Additional UNQ to SQL Capabilities 653 Prerequisites for Running the Examples 653 Using the LINQ to SQL API 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 Prerequisites for Running the Examples 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

13 GetStringFromDb() 675 ExecuteStatementlnDb() 676 Summary 677 Chapter 20: LINQ to Entities Operations. 679 Prerequisites for Running the Examples 679 Some Common Methods 679 Standard Database Operations 680 Inserts 680 Queries 687 Updates 704 Deletes Managing Concurrency 715 Enabling Concurrency Checks 716 Handling Concurrency Conflicts 717 Summary 722 Chapter 21: LINQ to Entities Classes 723 Prerequisites for Running the Examples 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

14 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

15 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