Linq query to return distinct values in xml

Question

I have an XML with the following structure:

<Categories>
  <Category>
    <Books>
      <Book>
        <BookId>1</BookId>
        <BookQuantity>150</BookQuantity>
      </Book>
      <Book>
        <BookId>2</BookId>
        <BookQuantity>250</BookQuantity>
      </Book>
    </Books>
  </Category>
  <Category>
    <Books>
      <Book>
        <BookId>1</BookId>
        <BookQuantity>150</BookQuantity>
      </Book>
      <Book>
        <BookId>3</BookId>
        <BookQuantity>250</BookQuantity>
      </Book>
    </Books>
  </Category>
</Categories>

I am trying to retrieve each distinct Book with its quantity within the category. The output would be:

Book 1 300
Book 2 250
Book 3 250

Any best method to do this. I tried with linq query but was not able to succeed.

Answer 1

You can use Linq to Xml . Query is simple - just select all Book elements and group them by value of BookId element. Then project each group into anonymous object or instance of book class:

var xdoc = XDocument.Load(path_to_xml);

var books = from b in xdoc.Root.Descendants("Book")
            group b by (int)b.Element("BookId") into g
            select new {
                Id = g.Key,
                Quantity = g.Sum(b => (int)b.Element("BookQuantity"))
            };

Result:

[
  { "Id": 1, "Quantity": 300 },
  { "Id": 2, "Quantity": 250 },
  { "Id": 3, "Quantity": 250 }
]

Instead of creating anonymous objects you can create instances of Book class:

public class Book
{
   public int Id { get; set; }
   public int Quantity { get; set; }
}