How to exclude null properties when using XmlSerializer

user_49885 0
Viewed 44249

I'm serializing a class like this

public MyClass
{
    public int? a { get; set; }
    public int? b { get; set; }
    public int? c { get; set; }
}

All of the types are nullable because I want minimal data stored when serializing an object of this type. However, when it is serialized with only "a" populated, I get the following xml

<MyClass ...>
    <a>3</a>
    <b xsi:nil="true" />
    <c xsi:nil="true" />
</MyClass>

How do I set this up to only get xml for the non null properties? The desired output would be

<MyClass ...>
    <a>3</a>
</MyClass>

I want to exclude these null values because there will be several properties and this is getting stored in a database (yeah, thats not my call) so I want to keep the unused data minimal.

xml-serialization nullable c#
10 Answers

If you make the class you want to serialise implement IXmlSerializable, you can use the following writer. Note, you will need to implement a reader, but thats not too hard.

    public void WriteXml(XmlWriter writer)
    {
        foreach (var p in GetType().GetProperties())
        {
            if (p.GetCustomAttributes(typeof(XmlIgnoreAttribute), false).Any())
                continue;

            var value = p.GetValue(this, null);

            if (value != null)
            {
                writer.WriteStartElement(p.Name);
                writer.WriteValue(value);
                writer.WriteEndElement();
            }
        }
    }
user_12091980

If you can accept the overhead that this would bring, rather than serializing directly to string, write to a LINQ XDocument directly where you can post process the serialization. Using regular expressions like the other answers suggest will be very brittle.

I wrote this method to return the LINQ object, but you can always call ToString() on it.

public XElement XmlSerialize<T>(T obj)
{
    var doc = new XDocument();
    var serializer = new XmlSerializer(typeof(T));
    using (var writer = doc.CreateWriter())
        serializer.Serialize(writer, obj);
    doc.Descendants()
        .Where(x => (bool?)x.Attribute(XName.Get("nil", "http://www.w3.org/2001/XMLSchema-instance")) == true)
        .Remove();
    return doc.Root!;
}
user_3902780
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