C# 4 and .NET 4

XMl and aDo.neT ❘ 927
To summarize, the key thing to keep in mind when performing transforms is to remember to use the proper
XML data store. Use XPathDocument if you do not need editing capabilities, XmlDataDocument if you are
getting your data from ADO.NET, and XmlDocument if you need to be able to edit the data. In each case,
you are dealing with the same process.
Xml and ado.neT
XML is the glue that binds ADO.NET to the rest of the world. ADO.NET was designed from the ground up
to work within the XML environment. XML is used to transfer the data to and from the data store and the
application or web page. Because ADO.NET uses XML as the transport in remoting scenarios, data can be
exchanged with applications and systems that are not even aware of ADO.NET. Because of the importance of
XML in ADO.NET, some powerful features in ADO.NET allow the reading and writing of XML documents.
The System.Xml namespace also contains classes that can consume or utilize ADO.NET relational data.
The database that is used for the examples is from the AdventureWorksLT sample application. The sample
database can be downloaded from codeplex.com/SqlServerSamples. Note that there are several versions
of the AdventureWorks database. Most will work, but the LT version is the simplified version and is more
than adequate for the purposes of this chapter.
Converting ado.neT data to Xml
The first example uses ADO.NET, streams, and XML to pull some data from the database into a DataSet,
load an XmlDocument object with the XML from the DataSet, and load the XML into a text box. To run
the next few examples, you need to add the following using statements:
using System.Data;
using System.Xml;
using System.Data.SqlClient;
using System.IO;
The connection string is defined as a module-level variable:
string _connectString = "Server=.\\SQLExpress;
Database=adventureworkslt;Trusted_Connection=Yes";
The ADO.NET samples have a DataGrid object added to the forms. This will allow you to see the data
in the ADO.NET DataSet because it is bound to the grid, as well as the data from the generated XML
documents that you load in the text box. Here is the code for the first example. The first step in the
examples is to create the standard ADO.NET objects to produce a DataSet object. After the data set has
been created, it is bound to the grid.
private void button1_Click(object sender, EventArgs e)
{
XmlDocument doc = new XmlDocument();
DataSet ds = new DataSet("XMLProducts");
SqlConnection conn = new SqlConnection(_connectString);
SqlDataAdapter da = new SqlDataAdapter
("SELECT Name, StandardCost FROM SalesLT.Product", conn);
//fill the dataset
da.Fill(ds, "Products");
//load data into grid
dataGridView1.DataSource = ds.Tables["Products"];
code snippet frmADOXML.cs
After you create the ADO.NET objects and bind to the grid, you instantiate a MemoryStream object, a
StreamReader object, and a StreamWriter object. The StreamReader and StreamWriter objects will use
the MemoryStream to move the XML around:
MemoryStream memStrm=new MemoryStream();
StreamReader strmRead=new StreamReader(memStrm);
StreamWriter strmWrite=new StreamWriter(memStrm);
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