LINQ , or L anguage IN tegrated Q uery, is set of classes added to the .NET Framework 3.5 along with language enhancements added to C# 3.0 and Visual Basic 9, the versions of the language that ship with Visual Studio 2008. LINQ adds a rich, standardized query syntax as a first-class citizen in .NET programming languages that allows developers to interact with any type of data. Consider a typical data-driven application. There may be times when you are working with a database, displaying records or editing, inserting, and deleting data. Certain parts of the application may require retrieving certain elements from an XML file, or constructing an XML file based on user input. Or perhaps you have a collection of objects returned from a business object that you now want to work with by sorting them, computing the average value of a particular numeric property value, and displaying only those objects that meet a specified criteria. Prior to LINQ, working with each data source requires writing a different style of code. Moreover, working with external resources like data bases, XML files, and the like typically involves communicating with that external resource in some syntax specific to that resource. To retrieve data from a database you need to send it a string that contains the SQL query to execute; likewise, to work with a subset of XML elements in an XML document involves specifying an XPath expression in the form of a string. The idea is that using LINQ you can work with disparate data sources using a similar style without having to know a separate syntax for communicating with the data source (e.g., SQL or XPath) and without having to resort to passing opaque strings to external resources. This article is the first in a series of articles that explores the goals of LINQ, its underpinnings, its syntax, and LINQ providers like LINQ to Objects, LINQ to XML, LINQ to SQL, and so forth
