Further Exploration with LINQ - Page 3
       by Granville Barnett  |  24 September 2007

In the previous page, we started exploring how LINQ and XML work with each other. In this page, let's continue by learning how you can use LINQ to make other XML tasks easier.

Updating Data
Updating XML data is also very simple, we just have to pick the element/attribute we wish to update and then set its new value. In this particular example we are just setting the value of the publisher attribute; when dealing with elements there are a host of methods we can use to do a similar operation.

XElement books = XElement.Load(@"Books.xml");

books.Element("book").Attribute("publisher").Value = "MS Press";

books.Save(@"Books.xml");

Deleting Data
Imagine you wake up one morning and suddenly feel the urge to get rid of all books of a particular publisher in your book collection – we will now construct the relevant LINQ query to do this:

XElement doc = XElement.Load("Books.xml");

doc.Descendants("book").Where(x => string)x.Attribute("publisher") == "MS Press").Remove();

doc.Save("Books.xml");

Here we pass a lambda expression in as an argument to the Where extension method. This lambda expression takes one argument (an XElement) and returns a Boolean depending on whether or not the attribute publisher of the book element is equal to MS Press.

Don’t be alarmed by the lambda expression argument to the Where extension method for now – we will cover lambda expressions later on in this article.

LINQ to SQL and LINQ to XML
So far we have looked at hard-coded XML – a great feature of LINQ to SQL is that we can actually generate an XML document directly from a query. The process of creating an XML document dynamically is very easy, and it’s something that I have grown to really appreciate ever since picking up the LINQ May 2006 CTP.

For our first example we will output the title of each book in the database:

BookShop db = new BookShop(_conn);

XElement titles = new XElement("titles", from b in db.GetBooks()

                                         select new XElement("title",

                                                              b.Title));
 

Console.WriteLine(titles);

The code generates an XML document with the structure shown in the following image:

[ the XML document you see when you print out titles ]

Here, instead of creating a new anonymous type like we may do when selecting specific properties of an entity, we create the appropriate XML types – constructing a perfect XML document while using a very small amount of code. I still get excited when I use this particular feature of LINQ to SQL, look at how much code we are writing. The simplicity of it is just great!

One of the concepts introduced in our last code snippet was the ability to actually nest a query within the definition of an XElement type. Our next example builds on this concept and introduces a second nested query so that we can loop through all the authors associated with any particular book:

XElement books = new XElement("books",
       from b in db.GetBooks()

         select new XElement("book", new XAttribute("publisher",

                                                     b.PublisherName),

                                     new XElement("title", b.Title),

                                     new XElement("authors",

                                       from a
                                     in db.GetAuthorByBookId(b.BookId)

                                       select new XElement("author",

                                                  a.AuthorName))));

 

Console.WriteLine(books);

The result of running the above code is shown below:

[ the results from running a nested query ]

Phew! As you can see, using LINQ with XML makes many common tasks, if not more easy, more elegant. In the next page, let's shift gears and talk a little about lambda expressions.

Onwards to the next page.

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