SUMMARY
LINQ provides the ability to perform SQL-like queries within Visual Basic. Depending on which form of LINQ you are using, the development environment may provide strong type checking and IntelliSense support.
LINQ to Objects allows a program to query arrays, lists, and other objects that implement the IEnumerable interface. LINQ to XML and the LINQ XML classes allow a program to extract data from XML objects and to use LINQ to generate XML hierarchies. LINQ to ADO.NET (which includes LINQ to SQL, LINQ to Entities, and LINQ to DataSet) allows a program to perform queries on objects representing data in a relational database. Together these LINQ tools allow a program to select data in powerful new ways.
Visual Basic includes many features that support LINQ. Extension methods, inline or lambda functions, anonymous types, type inference, and object initializers all help make LINQ possible. If misused, some of these features can make code harder to read and understand, but used judiciously, they give you new options for program development.
For much more information on the various LINQ technologies, see the online help and the web. The following list includes several useful Microsoft web pages that you can follow to learn more about LINQ. Some are a bit old but they still provide valuable information.
- Getting Started with LINQ in Visual Basic — http://msdn.microsoft.com/bb397910.aspx.
- Hooked on LINQ (a wiki with some useful information, particularly its “5 Minute Overviews”) — http://www.hookedonlinq.com/LINQtoSQL5MinuteOverview.ashx.
- LINQ to SQL — http://msdn.microsoft.com/bb386976.aspx.
- LINQ to SQL: .NET Language-Integrated Query for Relational Data — http://msdn.microsoft.com/bb425822.aspx.
- 101 Visual Basic LINQ Samples — http://msdn.microsoft.com/vstudio/bb688088.
- LINQ jump page — http://msdn.microsoft.com/bb397926.aspx.
- Visual Studio 2008 Code Samples — http://msdn.microsoft.com/vbasic/bb330936.aspx.
- Visual Studio 2010 Code Samples — http://msdn.microsoft.com/vstudio/dd238515.aspx.
- The .NET Standard Query Operators — http://msdn.microsoft.com/bb394939.aspx.
- Querying DataSets — Introduction to LINQ to DataSet (by Erick Thompson, ADO.NET Program Manager, in the ADO.NET team blog) — http://blogs.msdn.com/adonet/archive/2007/01/26/querying-datasets-introduction-to-linq-to-dataset.aspx.
- LINQ to SQL: .NET Language-Integrated Query for Relational Data — http://msdn.microsoft.com/bb425822.aspx.
- The ADO.NET Entity Framework Overview — http://msdn.microsoft.com/aa697427.aspx.
- Parallel LINQ (PLINQ) — http://msdn.microsoft.com/dd460688.aspx.
The last several chapters have explained how to build Visual Basic applications that run on the Microsoft Windows desktop, but Visual Basic programs can also run on the Windows Metro platform. Chapter 21 provides an introduction to building Metro-style applications. These applications use the same WPF ideas described in several earlier chapters.