Converting Data to XML with LINQ to XML
The XML document is constructed on the line that begins with Dim doc as
XDocument. The return type of the single statement is an
XDocument (an XML document). The
XDocument constructor is overloaded. One of its definitions is to accept a
ParamArray of objects. The idea here is that it is unknown how many actual arguments any particular document might require. In the statement in Listing 1 the XDocument is constructed with two arguments, an
XDeclaration and an
XDeclaration contains the XML document's metadata, and the
XElement defines the root node, "Customers". Each of the table rows represents a Customer as defined, and each Customer is a child node of the root, Customers. Only data that is part of the collection needs to be in the LINQ query.
The individual customer nodes are constructed using a LINQ query and represent
ParamArray arguments to the
XElement that represents the Customers node. The
From clause of the LINQ query defines the range variable
cust. The range variable is like the iterator variable in a
for loop. The
In clause contains the data source, in this case a collection of table rows. The
Order By clause sorts the results by CompanyName.
Selectclause--creates an XML element for each column in the Customer table. The XAttribute class will create an attribute from the CustomerID of the Customer row, and all of the other elements are child nodes of the Customer node. It's a bit of a complicated statement, but the statement that creates the
XDocumentis a single statement. If you look at the output in Listing 2 you will see that the organization of the construction statement mirrors the output.
One of capabilities of LINQ to XML is functional construction of an XML document. By using class constructors in the
System.Xml.Linq namespace and LINQ queries you can iterate over data, like a database table, and construct an XML document in a single statement.
BiographyPaul Kimmel is the VB Today columnist for CodeGuru.com and has written several books on object-oriented programming and .NET. Check out his upcoming book Professional DevExpress ASP.NET Controls (from Wiley) now available on Amazon.com and fine bookstores everywhere. Look for his upcoming book Teach Yourself the ADO.NET Entity Framework in 24 Hours (from Sams). You may contact him for technology questions at firstname.lastname@example.org. Paul Kimmel is a Technical Evangelist for Developer Express, Inc, and you can ask him about Developer Express at email@example.com and read his DX blog at http://community.devexpress.com/blogs/paulk.
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