Pro LINQ: Language Integrated Query in VB 2008

722 Pages·2009·4.189 MB·

by  Joseph C. Rattz Jr, Dennis Hayes (auth.)

Pro LINQ
Language Integrated Query
in VB 2008
Joseph C. Rattz, Jr. and Dennis Hayes
Pro LINQ: Language Integrated Query in VB 2008
Copyright © 2009 by Joseph C. Rattz, Jr. and Dennis Hayes
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Lead Editor: Ewan Buckingham
Technical Editor: Joseph C. Rattz, Jr.
Technical Reviewers: Joseph C. Rattz, Jr., Fabio Ferracchiati
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To my father-in-law, Samuel Arthur Sanders, I dedicate this book. Art Sanders was my
most supportive cheerleader while I was working on Pro LINQ: Language Integrated Query
in C# 2008. Unfortunately, Art’s health began to fail toward the end of that book, and for
a while, it seemed doubtful he would live to see it completed. Not one to give up, Art over-
came numerous hospitalizations and did indeed receive his personally signed copy.
Sadly, Art will never see this book because he passed away on February 25, 2009, at the
age of 80. Rest in peace, Art.
Contents at a Glance
About the Author ................................................................xxiii
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv
Acknowledgments ...............................................................xxvii
PART 1 Pro LINQ: Language Integrated Query
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
in VB.NET 2008
CHAPTER1 Hello LINQ ......................................................3
CHAPTER2 VB.NET 2008 Language Enhancements for LINQ .................21
PART 2 LINQ to Objects
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
CHAPTER3 LINQ to Objects Introduction ....................................81
CHAPTER4 Deferred Operators .............................................93
CHAPTER5 Nondeferred Operators ........................................177
PART 3 LINQ to XML
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
CHAPTER6 LINQ to XML Introduction ......................................241
CHAPTER7 The LINQ to XML API ..........................................247
CHAPTER8 LINQ to XML Operators ........................................337
CHAPTER9 Additional XML Capabilities ....................................369
iv
Part 4 LINQ to DataSet
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
CHAPTER 10 LINQ to DataSet Operators .....................................413
CHAPTER 11 Additional DataSet Capabilities ................................453
Part 5 LINQ to SQL
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
CHAPTER 12 LINQ to SQL Introduction .......................................463
CHAPTER 13 LINQ to SQL Tips and Tools ....................................477
CHAPTER 14 LINQ to SQL Database Operations ..............................505
CHAPTER 15 LINQ to SQL Entity Classes .....................................553
CHAPTER 16 The DataContext ..............................................599
CHAPTER 17 Concurrency Conflicts .........................................663
CHAPTER 18 Additional SQL Capabilities ....................................681
INDEX .......................................................................695
v
Contents
About the Author ................................................................xxiii
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv
Acknowledgments ...............................................................xxvii
PART 1 Pro LINQ: Language Integrated
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
Query in VB.NET 2008
CHAPTER1 Hello LINQ .....................................................3
A Paradigm Shift .................................................4
Query XML ..................................................4
Query a SQL Server Database .................................6
Introduction to LINQ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
LINQ Is About Data Queries ...................................8
Components ................................................8
LINQ to Objects .........................................8
LINQ to XML. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
LINQ to DataSet ........................................9
LINQ to SQL ............................................9
LINQ to Entities .........................................9
How to Obtain LINQ ..........................................9
LINQ Is Not Just for Queries .......................................10
Tips to Get You Started ...........................................13
Use Dim Without Specifying the Type When Confused ...........13
Use the Cast or OfType Operators for Legacy Collections. . . . . . . . .15
Prefer the OfType Operator to the Cast Operator ................16
Don’t Assume a Query Is Bug Free ...........................16
Take Advantage of Deferred Queries ..........................17
Use the DataContext Log ....................................18
Use the LINQ Forum .........................................19
Summary .......................................................19
vii
viii (cid:78)CONTENTS
CHAPTER2 VB.NET 2008 Language Enhancements for LINQ ..........21
New VB.NET 2008 Language Additions .............................21
New (and Not So New) Options ...............................22
Option Explicit .........................................22
Option Compare .......................................23
Option Strict. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Option Infer ...........................................24
Lambda Expressions ........................................24
Using Named Methods .................................25
Using Lambda Expressions ..............................26
Expression Trees ...........................................29
Keyword Dim, Object Initialization, and Anonymous Types .......30
The Implicitly Typed Local Variable Keyword Dim
(with Option Infer On/Option Strict On) .................31
Object Initialization Expressions. . . . . . . . . . . . . . . . . . . . . . . . . .33
Anonymous Types .....................................34
Extension Methods ..........................................38
Instance (Object) vs. Shared (Class) Methods Recap ........38
The Problem Solved by Extension Methods ................40
The Solution ..........................................41
Extension Method Declarations and Invocations ............42
Extension Method Precedence ...........................43
Partial Methods ............................................43
A Partial Method Example ...............................44
What Is the Point of Partial Methods? .....................46
The Rules .............................................47
Query Expressions ..........................................47
Query Expression Grammar .............................49
Query Expression Translation ............................51
Nullable Value Types ........................................60
XML Enhancements .........................................61
XML Literals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
XMLEmbedded Expressions ............................64
XML Axis Properties ....................................67
XML Namespace Imports ...............................74
Summary .......................................................77
(cid:78)CONTENTS ix
PART 2 LINQ to Objects
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CHAPTER3 LINQ to Objects Introduction ...............................81
LINQ to Objects Overview .........................................81
IEnumerable(Of T), Sequences, and the Standard Query Operators .....82
Returning IEnumerable(Of T) and Deferred Queries ..................83
Func Delegates .................................................87
The Standard Query Operators Alphabetical Cross-Reference .........88
A Tale of Two Syntaxes ..........................................90
Summary .......................................................90
CHAPTER4 Deferred Operators ..........................................93
Referenced Namespaces .........................................93
Referenced Assemblies ..........................................93
Query Expression Syntax vs. Standard Dot Notation Syntax ...........94
Common Classes ................................................94
The Deferred Operators by Purpose ................................96
Restriction .................................................96
Where ................................................96
Projection ..................................................99
Select ................................................99
SelectMany ..........................................105
Partitioning ...............................................110
Take ................................................110
TakeWhile ...........................................113
Skip .................................................115
SkipWhile ............................................116
Concatenation .............................................119
Concat ..............................................119
Ordering ..................................................122
OrderBy .............................................123
OrderByDescending ...................................129
ThenBy ..............................................132
ThenByDescending ...................................137
Reverse .............................................140
x (cid:78)CONTENTS
Join ......................................................142
Join .................................................142
GroupJoin ............................................144
Grouping .................................................146
GroupBy .............................................146
Set ......................................................152
Distinct ..............................................153
Union ...............................................154
Intersect .............................................156
Except ...............................................157
Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
Cast .................................................159
OfType ..............................................161
AsEnumerable ........................................164
Element ..................................................167
DefaultIfEmpty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
Generation ................................................172
Range ...............................................172
Repeat ..............................................173
Empty ...............................................174
Summary ......................................................175
CHAPTER5 Nondeferred Operators ....................................177
Referenced Namespaces ........................................177
Common Classes ...............................................177
The Nondeferred Operators by Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . .180
Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
ToArray ..............................................181
ToList ...............................................183
ToDictionary .........................................185
ToLookup ............................................190
Equality ..................................................195
SequenceEqual .......................................195
Element ..................................................199
First .................................................199
FirstOrDefault ........................................201
Last .................................................203
LastOrDefault ........................................205
Single ...............................................207
(cid:78)CONTENTS xi
SingleOrDefault .......................................209
ElementAt ...........................................211
ElementAtOrDefault ...................................212
Quantifiers ................................................213
Any .................................................214
All ..................................................216
Contains .............................................217
Aggregate ................................................220
Count ...............................................220
LongCount ...........................................222
Sum ................................................224
Min .................................................226
Max .................................................229
Average .............................................232
Aggregate ...........................................234
Summary ......................................................238
PART 3 LINQ to XML
(cid:78)(cid:0)(cid:78)(cid:0)(cid:78)
CHAPTER6 LINQ to XML Introduction ..................................241
Additional Advantages of LINQ to XML .............................244
Cheating the W3C DOM XML API .................................244
Summary ......................................................246
CHAPTER7 The LINQ to XML API .......................................247
Referenced Namespaces ........................................247
Significant API Design Enhancements .............................248
XML Tree Construction Simplified with
FunctionalConstruction ..................................248
Document Centricity Eliminated in Favor of
Element Centricity .......................................251
Names, Namespaces, and Prefixes ..........................253
Node Value Extraction ......................................255
The LINQ to XML Object Model ...................................258
Deferred Query Execution, Node Removal, and
the Halloween Problem .......................................259