Introducing Query Expressions in Visual C#.NET

Creator QR Code JIS X 0510 in Visual C#.NET Introducing Query Expressions
Introducing Query Expressions
Draw QR Code In C#
Using Barcode maker for .NET framework Control to generate, create QR Code 2d barcode image in .NET applications.
static void List1(string rootDirectory, string searchPattern) { IEnumerable<FileInfo> files = from fileName in DirectoryGetFiles( rootDirectory, searchPattern) select new FileInfo(fileName); foreach (FileInfo file in files) { ConsoleWriteLine("{0}({1})", fileName, fileLastWriteTime); } } //
Barcode Generator In Visual C#
Using Barcode generator for Visual Studio .NET Control to generate, create bar code image in .NET applications.
OUTPUT 152:
Creating Quick Response Code In .NET
Using Barcode generator for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
Accountcs(11/22/2007 11:56:11 AM) Billcs(8/10/2007 9:33:55 PM) Contactcs(8/19/2007 11:40:30 PM) Customercs(11/17/2007 2:02:52 AM) Employeecs(8/17/2007 1:33:22 AM) Personcs(10/22/2007 10:00:03 PM)
Creating Denso QR Bar Code In VS .NET
Using Barcode creator for Visual Studio .NET Control to generate, create QR Code image in .NET framework applications.
Notice that this query expression returns an IEnumerable<FileInfo> rather than the IEnumerable<string> data type returned by SystemIODirectoryGetFiles() The select clause of the query expression can potentially project out a data type that is different from what was collected by the from clause expression (DirectoryGetFiles()) In fact, projection such as this is the key driving factor for why C# 30 includes anonymous types within the language Via anonymous types, it becomes possible to select out the exact data you seek without having to define an explicit type For example, Listing 153 provides output similar to that in Listing 152, but via anonymous types rather than FileInfo
Drawing QR Code 2d Barcode In Visual Basic .NET
Using Barcode generation for VS .NET Control to generate, create QR Code 2d barcode image in .NET applications.
Listing 153: Anonymous Types within Query Expressions
Drawing Barcode In C#
Using Barcode creator for VS .NET Control to generate, create barcode image in Visual Studio .NET applications.
using using using using System; SystemCollectionsGeneric; SystemLinq; SystemIO;
Bar Code Generation In Visual C#.NET
Using Barcode printer for .NET framework Control to generate, create barcode image in .NET applications.
// static void List2(string rootDirectory, string searchPattern) {
Drawing Code 39 Full ASCII In C#.NET
Using Barcode creator for .NET framework Control to generate, create Code 39 image in VS .NET applications.
15: LINQ with Query Expressions
Code 128 Code Set B Creator In C#
Using Barcode generator for .NET framework Control to generate, create ANSI/AIM Code 128 image in Visual Studio .NET applications.
var files = from fileName in DirectoryGetFiles( rootDirectory, searchPattern) select new { Name = fileName, LastWriteTime = FileGetLastWriteTime(fileName) }; foreach (var file in files) { ConsoleWriteLine("{0}({1})", fileName, fileLastWriteTime); } } //
Data Matrix 2d Barcode Encoder In C#
Using Barcode drawer for .NET framework Control to generate, create Data Matrix image in VS .NET applications.
In this example, the query projects out only the filename and its last file write time A projection such as the one in Listing 153 makes little difference when working with something small such as FileInfo However, horizontal projection that filters down the amount of data associated with each item in the collection is extremely powerful when the amount of data is significant and retrieving it (perhaps from a different computer over the Internet) is expensive Rather than retrieving all the data when a query executes, the use of anonymous types enables the capability of storing and retrieving only the required data into the collection Imagine, for example, a large database that has tables with 30 or more columns If there were no anonymous types, developers would be required to either use objects containing unnecessary information or define small, specialized classes useful only for storing the specific data required Instead, anonymous types enable support for types to be defined by the compiler types that contain only the data needed for their immediate scenario Other scenarios can have a different projection of only the properties needed for that scenario
DataMatrix Printer In Visual Studio .NET
Using Barcode creation for Visual Studio .NET Control to generate, create Data Matrix 2d barcode image in .NET framework applications.
BEGINNER TOPIC Deferred Execution with Query Expressions The topic of deferred execution appeared in the preceding chapter as well The same principles also apply to query expressions Consider again the assignment of selection in Listing 151 The assignment itself does not
Generating ECC200 In Java
Using Barcode generation for Java Control to generate, create Data Matrix ECC200 image in Java applications.
Introducing Query Expressions
Bar Code Encoder In Visual Basic .NET
Using Barcode maker for .NET framework Control to generate, create barcode image in Visual Studio .NET applications.
execute the query expression In other words, during the assignment of selection, wordContains("*") is not called Rather, the query expression saves off the selection criteria to be used when iterating over the collection identified by the selection variable To demonstrate this point, consider Listing 154 and the corresponding output (Output 153)
Barcode Maker In .NET
Using Barcode printer for .NET framework Control to generate, create bar code image in .NET applications.
Listing 154: Deferred Execution and Query Expressions (Example 1)
Generate EAN-13 Supplement 5 In .NET
Using Barcode drawer for ASP.NET Control to generate, create UPC - 13 image in ASP.NET applications.
using System; using SystemCollectionsGeneric; using SystemLinq; // private static void ShowContextualKeywords2() { IEnumerable<string> selection = from word in Keywords where IsKeyword(word) select word; foreach (string keyword in selection) { ConsoleWrite(keyword); } } // Side effect (console output) included in predicate to show // deferred execution not as a best practice private static bool IsKeyword(string word) { if (wordContains('*')) { ConsoleWrite(" "); return true; } else { return false; } } //
Code-39 Printer In VS .NET
Using Barcode drawer for .NET framework Control to generate, create Code-39 image in Visual Studio .NET applications.
OUTPUT 153:
Code 3 Of 9 Drawer In Visual Basic .NET
Using Barcode maker for .NET framework Control to generate, create Code-39 image in .NET framework applications.
add* alias* ascending* by* descending* dynamic* equals* from* get* global* group* into* join* let* on* orderby* partial* remove* select* set* value* var* where* yield*
Drawing Code 128 Code Set A In VS .NET
Using Barcode generation for VS .NET Control to generate, create Code-128 image in .NET framework applications.
15: LINQ with Query Expressions
Barcode Recognizer In Visual Studio .NET
Using Barcode scanner for .NET framework Control to read, scan read, scan image in .NET framework applications.
Notice that in Listing 154, no space is output within the foreach loop The space between the contextual keywords is output in the IsKeyword() function, demonstrating that the IsKeyword() function isn t called until the code iterates over selection rather than when selection is assigned The point is that although selection is a collection (it is of type IEnumerable<T> after all), at the time of assignment everything following the from clause comprises the selection criteria Not until we begin to iterate over selection are the criteria applied Consider a second example (see Listing 155 and Output 154)
Create Universal Product Code Version A In .NET Framework
Using Barcode creation for ASP.NET Control to generate, create GS1 - 12 image in ASP.NET applications.
Listing 155: Deferred Execution and Query Expressions (Example 2)
using System; using SystemCollectionsGeneric; using SystemLinq; // private static void CountContextualKeywords() { int delegateInvocations = 0; Func<string, string> func = text=> { delegateInvocations++; return text; }; IEnumerable<string> selection = from keyword in Keywords where keywordContains('*') select func(keyword);
ConsoleWriteLine( "1 delegateInvocations={0}", delegateInvocations); // Executing count should invoke func once for // each item selected ConsoleWriteLine( "2 Contextual keyword count={0}", selectionCount()); ConsoleWriteLine( "3 delegateInvocations={0}", delegateInvocations); // Executing count should invoke func once for