MSDN Magazine - July 2008 - (Page 35)

KEN GETz AdvAnced BAsics The LINQ Enumerable Class, Part 1 As part of a recent programming project, I needed to create a ran domly ordered list of integers between 1 and 100. Yes, this is obvi ously a basic Computer Science 101type problem. And I originally used the same solution I had written back in the classroom, in 1985, using lots of looping and comparisons and generating ran dom numbers and several arrays. But in these days of declarative programming, the solution really bothered me. After some research, I managed to whittle the problem down to just two lines of code: Dim rnd As New System.Random() Dim numbers = Enumerable.Range(1, 100). _ OrderBy(Function() rnd.Next) in context of LINQ to SQL, you’re actually calling extension meth ods on the LINQ to SQL provider’s Queryable class that have the same signatures as the methods shown here. Although such ex amples would illustrate the same behavior, they wouldn’t be using the Enumerable class.) I strongly suggest that you download the sample application and follow along using this application—the code will make much more sense if you can experiment with it directly, rather than just reading it here. To make the long list of methods more tractable, I’ve broken them down into logical groupings. You’ll investigate methods that After running these two lines, the numbers variable contains the integers between 1 and 100, in random order. The behavior of this simple yet elegant solution counts on the System.Linq.Enumerable class, which provides a few dozen shared methods called extension methods that allow you to manipulate data in any class that implements the IEnumerable(Of T) inter face. In addition, as you see in this example, these methods also can generate new collections of data. In this and my next column, I will provide examples of the Enu merable class’s extension methods, showing off multiple overloaded versions of the members and using various data structures to dem onstrate the capabilities. Because you can apply these methods in so many places, and because they’re so incredibly useful, it makes sense to take some time and investigate each—that way, when you need to operate on a collection, you’ll know what tools you have available to you. I’ve created a simple Windows®based application as a sample. In the project, I’ve added simple classes representing the Custom ers, Categories, and Products data, and I’ve added a class named SimpleDataContext that fills instances of the these classes with data from the SQL Server® Northwind sample database. In addi tion, this class exposes public properties named Customers, Cat egories, and Products; each containing a generic List of Customer, Category, and Product instances, respectively. (Although I could have used the LINQ to SQL designer to create a “real” DataContext class, doing so wouldn’t allow me to demonstrate the Enumerable class’s extension methods: when you call the described methods Send your questions and comments for Ken to basics@microsoft.com. Code download available at msdn.microsoft.com/magazine/cc135911. The Enumerable class plays an important role in every LINQ query that you create. deal with creating, selecting, retrieving a single element, filtering, converting, positioning within sequences, ordering, verifying, cal culating, and performing set operations of sequences of data. In each of the following sections, you’ll try out various examples that demonstrate one or more methods of the Enumerable class. By the time you’re done, you will have worked through all the methods of the Enumerable class, and you will have investigated many of the overloads for the more complicated methods. Note that the examples generally allow Visual Basic® to infer data types, rather than having the code specify the type of the return value for calls to the extension methods on the Enumerable class. Also, the sample relies on the Northwind sample database, installed on SQL Express. If you want to run the sample, you’ll either need to replicate this environment or modify the sample application. Inside Enumerable The Enumerable class plays an important role in every LINQ query you create. For example, imagine that your project includes a Product class and a generic List of Product instances (as in the sample project). You’ve created an instance of the SimpleData Context class from the sample that fills data in the Products list, and you write a query like this: Dim db As New SimpleDataContext() Dim query = _ July 2008 35 http://msdn.microsoft.com/magazine/cc135911

Table of Contents Feed for the Digital Edition of MSDN Magazine - July 2008

MSDN Magazine - July 2008 Contents Toolbox CLR Inside Out Flex Your Data Data Points Advanced Basics Office Space Cutting Edge Data Services ADO.NET Data and WPF Transactions WCF P2P Test Run Security Briefs Foundations .NET Matters {End Bracket}

MSDN Magazine - July 2008

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