MSDN Magazine - March 2008 - (Page 21)

Standard Query Operators with LINQ JOHN PAPA anguage Integrated Query (LINQ) allows developers to write SQL-like queries with Microsoft® .NET Framework 3.5 code using a strongly typed syntax. Different LINQ providers, such as LINQ to Objects (which allows you to write queries against object hierarchies) and LINQ to Entities (which allows you to write queries against the Entity Framework’s conceptual model), are then able to effectively process these queries according to the nuances of their representative data stores. Besides the strongly typed syntax, LINQ queries also have an arsenal of standard query operators to enhance their functionality. These standard query operators operate on sequences and allow you to perform operations such as determining if a value exists in the sequence and performing an aggregated function, such as a summation, over a sequence. In this month’s column I will perform practical queries and operations with LINQ, using both LINQ to Objects and LINQ to Entities. I’ll query a single collection of entities and dive deeper into a hierarchical set of entities using their navigation properties. I’ll also show how you can apply many of the standard query operators to arrays and collections. I will demonstrate how LINQ’s standard query operators are enhanced using lambda expressions and how they can let you parse specific information from a sequence and perform complex logic over a sequence. All code examples are available in the download provided for this column (see msdn.microsoft.com/msdnmag/code08.aspx). L disposal for a specific task. When you want to use an operator in a LINQ query, you can use an operator from the available list of extension methods in the Queryable static class. When you When LINQ is combined with want to use an operator on one or more standard query a sequence that implements operators, the result is an IEnumerable , you can use one of the extension even more powerful toolset methods found in the Enuthat can give you granular merable static class. Keep control over a set of data. in mind, however, that not all of the operators found in the Queryable class are applicable to the underlying data store, and hence some may not be supported at run time. Types of Operators There are many different types of operators (all of which can be found using the object browser to look at the Enumerable and Queryable classes). Figure A (which can be found at msdn.microsoft.com/ msdnmag/issues/08/03/DataPoints/#figA) shows a categorization of the different types of operators in alphabetical order. It offers you a glimpse at the functionality the operators provide. I will be demonstrating a subset of these operators using both LINQ to Objects and LINQ to Entities to show how they can be beneficial in a realworld application. Operators and LINQ LINQ is very powerful all on its own whether you are using LINQ to XML, LINQ to DataSets, LINQ to Entities, LINQ to Objects, or any other LINQ provider that comes along. The core power of LINQ is in its strongly typed query syntax, which can be used to operate over any of these providers. When LINQ is combined with one or more standard query operators, the result is an even more powerful toolset that can give you granular control over a set of data. Standard query operators exist in the System.Core.dll assembly within the System.Linq namespace as extension methods on the static classes Enumerable and Queryable, and they can be used on objects that implement IEnumerable or IQueryable . This allows them to operate on a variety of types, from in-memory collections and arrays (sequences) to remote databases using providers like LINQ to Entities and LINQ to SQL. It is easy to determine which set of operators you have at your Lambda Expressions Many standard query operators use Func delegates to process individual elements as they operate over a sequence. Lambda expressions can work in concert here with the standard query operators to represent the delegates. A lambda expression is a shorthand form for creating an implementation of a delegate and can be used anywhere an anonymous delegate can be used. Lambda expressions are supported by both C# and Visual Basic® .NET. It is important to note, though, that because Visual Basic .NET does not yet support anonymous methods, lambda expressions may consist of only a single statement. Let’s see how the Single operator can be used on an array of integers. An array of integers, each element representing a power of 2 from 1 through 10, is created and then the Single operator is This column is based in part on a prerelease version of the ADO.NET Entity Framework. Details herein are subject to change. march2008 21 http://msdn.microsoft.com/msdnmag/issues/08/03/DataPoints/#figA http://msdn.microsoft.com/msdnmag/issues/08/03/DataPoints/#figA http://msdn.microsoft.com/msdnmag/code08.aspx http://msdn.microsoft.com/msdnmag/code08.aspx

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

MSDN Magazine - March 2008 Contents Toolbox CLR Inside Out Data Points Advanced Basics Office Space Introducing ASP.NET MVC Loosen Up CI Server Performance Office Development Test Run Security Briefs Extreme ASP.NET Foundations .NET Matters {End Bracket}

MSDN Magazine - March 2008

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