Only output XML elements that are set when serializing

Question

I have the following XML:

<Line id="6">
  <item type="product" />
  <warehouse />
  <quantity type="ordered" />
  <comment type="di">Payment by credit card already received</comment>
</Line>

Is there a way to not output the elements that aren't set when serializing an object in .NET (2010 with C#)? In my case, the item type, the warehouse, the quantity so that I end up with the following instead when serialized:

<Line id="6">
  <comment type="di">Payment by credit card already received</comment>
</Line>

I can't see any properties in the XmlElement or XmlAttribute that would let me achieve this.

Is XSD required? If it is, how would I go about it?

Answer 1

For simple cases, you can usually use [DefaultValue] to get it to ignore elements. For more complex cases, then for any member Foo (property / field) you can add:

public bool ShouldSerializeFoo() {
    // TODO: return true to serialize, false to ignore
}
[XmlElement("someName");
public string Foo {get;set;}

This is a name-based convention supported by a number of frameworks and serializers.

For example, this writes just A and D:

using System;
using System.ComponentModel;
using System.Xml.Serialization;

public class MyData {
    public string A { get; set; }
    [DefaultValue("b")]
    public string B { get; set; }
    public string C { get; set; }

    public bool ShouldSerializeC() => C != "c";

    public string D { get; set; }

    public bool ShouldSerializeD() => D != "asdas";

}
class Program {
    static void Main() {
        var obj = new MyData {
            A = "a", B = "b", C = "c", D = "d"
        };
        new XmlSerializer(obj.GetType())
            .Serialize(Console.Out, obj);
    }
}

B is omitted because of [DefaultValue]; C is omitted because of the ShouldSerializeC returning false.