Question

Having trouble trying to turn an XDocument into an list of objects, in particular the Categories element. Below is a snippet of the XML which returns a list of shows in the following format.

<Show>
  <Name>OLYMPIC GAMES</Name>
  <Artist>OLYMPIC GAMES</Artist>
  <OnSale>false</OnSale>
  <DateOnSale>2011-03-11T00:00:00</DateOnSale>
  <DoorsOpen>2012-12-31T10:00:00</DoorsOpen>
  <Starts>2012-12-31T10:00:00</Starts>
  <BespokeDate>25 July 2012 - 12 August 2012</BespokeDate>
  <Status Code="3">SOLD OUT</Status>
  <Categories>
    <Category Id="190">OTHER</Category>
  </Categories>
  <Prices>
    <Price Type="1">
      <Status Code="24">ORDER</Status>
      <FaceValue>0.00</FaceValue>
      <BookingFee>0.00</BookingFee>
      <TicketPrice>0.00</TicketPrice>
      <Description>UNRESERVED</Description>
    </Price>
  </Prices>
  <Venue Uri="/venues/">
    <Name>Various venues</Name>
    <Town></Town>
  </Venue>
</Show>

Below is the classes I have created to model the XML data

public class Show {
  public string Name { get; set; }
  public string Artist { get; set; }
  public bool OnSale { get; set; }
  public DateTime DateOnSale { get; set; }
  public DateTime DoorsOpen { get; set; }
  public DateTime Starts { get; set; }
  public string BespokeDate { get; set; }
  public Status Status { get; set; }
  public IEnumerable<Category> Categories { get; set; }
  public Venue Venue { get; set; }
}

public class Status
{
  public int Code { get; set; }
  public string Description { get; set; }
}

public class Category
{
  public int Id { get; set; }
  public string Name { get; set; }
}

public class Venue
{
  public string Uri { get; set; }
  public string Name { get; set; }
  public string Town { get; set; }
}

Below is the Linq to XML to create the Show objects

var shows = from s in xdoc.Descendants("Show")
  where 
    s.Element("OnSale").Value.AsBool() != false
  select
    new Show {
      Name = s.Element("Name").Value,
      Artist = s.Element("Artist").Value,
      OnSale = s.Element("Name").Value.AsBool(),
      DateOnSale = s.Element("DateOnSale").Value.AsDateTime(),
      DoorsOpen = s.Element("DoorsOpen").Value.AsDateTime(),
      Starts = s.Element("Starts").Value.AsDateTime(),
      BespokeDate = s.Element("BespokeDate").Value,
      Status = new Status { 
        Code = s.Element("Status").Attribute("Code").Value.AsInt(),
        Description = s.Element("Status").Value
      },
      Categories = (from c in s.Element("Categories").Elements("Category")
        select new Category { 
            Id = s.Attribute("Id").Value.AsInt(),
            Name = s.Value
          }),
      Venue = new Venue {
        Name = s.Element("Venue").Element("Name").Value,
        Town = s.Element("Venue").Element("Town").Value
      }
};

Below is the code snippet to display a Show

foreach(var show in shows)
{
  <p>
    Name: @show.Name | 
    Status: @show.Status.Description | 
    Venue: @show.Venue.Name | 
    Categories: @string.Join(",", show.Categories.Select(x => x.Name))
  </p>
}

The following error appears “Object reference not set to an instance of an object”, whenever attempting to display categories. From what I can see, every show has 1 or more categories.

Any ideas?

Answer 1

This is the problem:

  Categories = (from c in s.Element("Categories").Elements("Category")
    select new Category { 
        Id = s.Attribute("Id").Value.AsInt(),
        Name = s.Value
      }),

You’re using s.Attribute and s.Value instead of c.Attribute and c.Value.

I would also suggest using the explicit conversion to int instead of Value.AsInt():

  Categories = (from c in s.Element("Categories").Elements("Category")
    select new Category { 
        Id = (int) c.Attribute("Id"),
        Name = (string) c.Value
      }),