Executing a Simple DLinq Query
Now that you've seen how DLinq maps classes to tables and properties to columns, here's a simple example that uses DLinq to retrieve relational data, transforms that into XML data using XLinq, and finally displays the XML data by data binding with an XmlDataSource control.
To start, create a new Web site named
AdvancedXLinq using the LINQ ASP.NET Web Site template. After creating the Web site, add the
AdventureWorks.cs file created in the previous section to the
App_Code folder of the new Web site. After that, create a new ASP.NET page and modify its code as shown in
Listing 1. Note that in addition to the core LINQ and XLinq namespaces such as System.Query and System.Xml.XLinq, you also need to import the System.Data.DLinq namespace to use DLinq features from the code.
The
Page_Load event retrieves the connection string from the Web.config file, passing that to the SqlConnection object constructor:
SqlConnection connection = new SqlConnection(connectionString);
After creating the SqlConnection object, you supply that as an argument to the constructor of the AdventureWorks class:
AdventureWorks db = new AdventureWorks(connection);
With this plumbing in place, you can now query any table in the AdventureWorks database using the familiar LINQ query notation. As an example, you can retrieve all the categories from the
ProductCategory table just by using the format
db.Production.ProductCategory. This example retrieves all the categories and transforms them into XML format using the XLinq functional construction technique discussed in
Part 1 of this series:
XElement categories = new XElement("Categories",
from category in db.Production.ProductCategory
select new XElement("Category",
new XAttribute("ID", category.ProductCategoryID),
new XAttribute("Name", category.Name),
new XAttribute("Guid", category.Rowguid)));
As discussed in
Part 2 of this article series, the
from…select query retrieves all the categories. You then transform each of the category values into attributes of an XML element named
<Category>, which in turn is embedded inside a root
<Categories> element. The preceding code generates the following XML:
<Categories>
<Category ID="1" Name="Bikes"
Guid="cfbda25c-df71-47a7-b81b-64ee161aa37c" />
---
---
</Categories>
 | |
| Figure 1. Categories Output: Here's the output of Listing 1, showing the list of categories retrieved from the AdventureWorks database. |
To databind the returned XML with an XmlDataSource, set its
Data property to the output XML:
categorySource.Data = categories.Xml;
Finally you set the
DataSource property of the GridView control to the ID of the XmlDataSource and then invoke its
DataBind() method:
gridCategories.DataSource = categorySource;
gridCategories.DataBind();
Figure 1 shows the output produced by the page when requested from the browser.
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