Developer: Query style programming with Orcas

Query style programming with Orcas

Developers can now apply standard query operators in their programs using LINQ with Visual Studio 2008 (Orcas) to directly access the data objects

Rahul Sah

Thursday, November 08, 2007

LINQ to Objects

LINQ to Objects refers to LINQ expressions used for in-memory objects such as arrays or datasets. To see Language Integrated Query at work, let's create a new project in Visual Studio 2008. Go to File>New Project and under Project Type select Visual Basic's Windows project of type Windows Form Application and name it as LinqDemo1, with this Form1.vb gets created. In the following example we will try populating a DataGridView with information on files in a directory: 'E:/docs' in our case. First drop a DataGridView from Toolbox pane onto the Form1 and dock it onto the parent container.

Double clicking on the Form1 will show the code window, where on Form Load event we will first try retrieving the file information of the directory E:/docs. Using LINQ, we will now write code in query format to retrieve the file information. The following code snippet does the same; the file info will be retrieved for the directory and stored in 'files' variable.

Dim files = From file In My.Computer.FileSystem.GetFiles("E:\docs") Order By file Select file

The LinqDemo example lists the file information in directory 'E:/docs' upon execution of application

The variable 'files' would contain IEnumerable of String objects. The compiler automatically gets to know the type of result the query would return. And the variable is automatically type-casted according to returned result, thus variable would be having all the file names from the directory. Once we have the file names, we would now display file information on DataGridView as a list.

For this we will again use FileSystem to get the file information. With GetFileInfo of FileSystem we get all the attributes related to a file, like name, creation time, size etc. If we were not to use LINQ here, it would have required getting a Collection of FileInfo objects and then using loop we would have retrieved values to store into an array. With query-based coding, a developer can use LINQ to traverse and retrieve objects.

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