Web API - Self close tag instead of i:nil

Question

I am using Web API with DataContract serialization. The output looks like this:

<Data>
<Status>
  <Date>2014-08-13T00:30:00</Date>
  <ID>312</ID>
  <Option>No Limitation</Option>
  <Value i:nil="true" />
</Status>
<Status>
  <Date>2014-08-13T01:00:00</Date>
  <ID>312</ID>
  <Option>No Limitation</Option>
  <Value i:nil="true" />
</Status>
<Status>
  <Date>2014-08-13T01:30:00</Date>
  <ID>312</ID>
  <Option>No Limitation</Option>
  <Value i:nil="true" />
</Status>
<Status>
  <Date>2014-08-13T02:00:00</Date>
  <ID>312</ID>
  <Option>No Limitation</Option>
  <Value i:nil="true" />
</Status>

I was able to remove all the extra namespaces by doing:

[DataContract(Namespace="")]
public class Status

But the only attribute left is the i:nil attribute. What should i do in order to remove the i:nil attribute?

Braw

Would this solve your problem: #12465785, DataMember(EmitDefaultValue = false)] – Bowman

@Prescott, that will remove the empty element at all. What I want is to show the element without the i:nil attribute. – Braw

Answer 1

What you want is to make the code "think" that instead of having a null value, it actually has an empty string. You can do that by being a little smart with the property getter (see below). Just remember to add a comment explaining why you're doing that so other people who will maintain the code know what's going on.

[DataContract(Namespace = "")]
public class Status
{
    [DataMember]
    public DateTime Date { get; set; }

    [DataMember]
    public int ID { get; set; }

    [DataMember]
    public string Option { get; set; }

    private string value;

    [DataMember]
    public string Value
    {
        get { return this.value ?? ""; }
        set { this.value = value; }
    }
}

Exocarp

Simple and nice. That was exactly what I needed, Thanks. – Braw

Great, works for me. After this change I had to change the code that uses this value from Value != null to string.IsNullOrEmpty(Value) – Lumpfish

Answer 2

You need to set the EmitDefaultValue property in the DataMember attribute

[DataMember(EmitDefaultValue = false)]

Be sure not to set this attribute on members that have the IsRequired = true set to them.

Edit

You may also iterate the XML manually and remove the nil attributes using LINQ 2 XML:

XNamespace i = "http://www.w3.org/2001/XMLSchema-instance";
        XDocument xdoc = XDocument.Load(@"XmlHere"); // This may be replaced with XElement.Parse if the XML is in-memory

        xdoc.Descendants()
                 .Where(node => (string)node.Attribute(i + "nil") == "true")
                 .Remove();

Loosejointed

That will remove the empty element at all, isn't it? I want to show the element but without the i:nil attribute. – Braw

It will remove any null element, yes. I edited my answer with a way to manually remove the specified attributes. – Loosejointed

What you are proposing is right, but in the case of Web API, you can't manipulate the XML like this, it is an internal serialization. – Braw

You can by implementing IXmlSerializable yourself. – Loosejointed

Take a look at this – Loosejointed

That will force me to use XmlSerializer but I need to use DataContract. Is there a way to remove i:nil attribute using DataContract? – Braw

I haven't ever done that with DataContractSerializer. Sorry. – Loosejointed