How can I deserialize heterogeneous child nodes into a collection, using XmlSerializer?

Question

I'm using C#/.NET to deserialize a XML file that looks akin to this:

<?xml version="1.0" encoding="utf-8" ?>
<Books>
  <Book
    Title="Animal Farm"
    >
    <Thing1>""</Thing1>
    <Thing2>""</Thing2>
    <Thing3>""</Thing3>
    ...
    <ThingN>""</ThingN>
  </Book>
  ... More Book nodes ...
</Books>

My classes, for the deserialized XML, look like:

[XmlRoot("Books")]
public class BookList
{
    // Other code removed for compactness. 

    [XmlElement("Book")]
    public List<Book> Books { get; set; }
}

public class Book
{
    // Other code removed for compactness. 

    [XmlAttribute("Title")]
    public string Title { get; set; }

    [XmlAnyElement()]
    public List<XmlElement> ThingElements { get; set; }

    public List<Thing> Things { get; set; }
}  

public class Thing
{
    public string Name { get; set; }
    public string Value { get; set; }
} 

When deserializing, I want all the child nodes of the Book element (<Thing1> through <ThingN>) to be deserialized into a Book's Things collection. However, I'm unable to figure out how to accomplish that. Right now, I'm stuck storing the Thing nodes in the ThingElements collection (via XmlAnyElement).

Is there a way to deserialize heterogeneous child nodes into a collection (of non-XmlElements)?

Answer 1

If you wanted to serialize this as a set of simple KeyValuePairs you could use a custom Struct to accomplish this. Unfortunately the built in generic KeyValuePair won't work.

But, given the following class definitions:

[XmlRoot("Books")]
public class BookList
{
    [XmlElement("Book")]
    public List<Book> Books { get; set; }
}

public class Book
{
    [XmlAttribute("Title")]
    public string Title { get; set; }

    [XmlElement("Attribute")]
    public List<AttributePair<String, String>> Attributes { get; set; }
}

[Serializable]
[XmlType(TypeName = "Attribute")]
public struct AttributePair<K, V>
{
    public K Key { get; set; }
    public V Value { get; set; }

    public AttributePair(K key, V val)
        : this()
    {
        Key = key;
        Value = val;
    }
}

When I serialize an object using this information I get an XML structure that looks something like this.

<?xml version="1.0"?>
<Books xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
       xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Book Title="To win a woman">
    <Attribute>
      <Key>Author</Key>
      <Value>Bob</Value>
    </Attribute>
    <Attribute>
      <Key>Publish Date</Key>
      <Value>1934</Value>
    </Attribute>
    <Attribute>
      <Key>Genre</Key>
      <Value>Romance</Value>
    </Attribute>
  </Book>
</Books>

I am also able to successfully read that XML right back into an object and print out the information.

You can test it out for yourself in a console application to see the results.

using(var file = File.OpenRead("booklist.xml"))
{
    var readBookCollection = (BookList)serializer.Deserialize(file);

    foreach (var book in readBookCollection.Books)
    {
        Console.WriteLine("Title: {0}", book.Title);

        foreach (var attributePair in book.Attributes)
        {
            Console.CursorLeft = 3;
            Console.WriteLine("Key: {0}, Value: {1}", 
                attributePair.Key, 
                attributePair.Value);
        }
    }
}