Can asmx services return nothing instead of null?

Question

Hey all,

I have a WebService I'm maintaining, running on .Net 2.0. It uses the original "asmx" file standard for a series of web services. In these web services, some objects are returned that have potentially a large number of "null" values. For example:

<user id="1" name="foo" job="null" location="null" audience="null" />

This is a simple example; in reality, we have a lot more "null" values. Since I don't really need to have the nulls because I can easily infer that they're null from their non-existence, I'd prefer to not return them at all. Can this be done? If so, how?

Edited to add class definition:

[Serializable]
public partial class User

    [XmlAttribute("Id")]
 public int Id 
 {
  get { return GetColumnValue<int>("ID"); }

  set { SetColumnValue("ID", value); }

 }



 [XmlAttribute("Username")]
 public string Username 
 {
  get { return GetColumnValue<string>("Username"); }

  set { SetColumnValue("Username", value); }

 }
}

By the way, what I'm aiming to see is:

<user id="1" name="foo" />

Answer 1

XmlElementAttribute.IsNullable Property

If the IsNullable property is false, no XML element is generated for class members that have been set to a null reference (Nothing in Visual Basic).

public class MyClass
{
   [XmlElement(IsNullable = false)]
   public string Group;
}

Answer 2

From a schema perspective you are effectively saying that the elements are optional, this can be achieved ( at least according to the documentation ) through use of the DefaultValue attribute. See http://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlattributes.xmldefaultvalue.aspx

Answer 3

The example xml is confusing, because in most cases the serializer will omit nulls, especially for attributes. The exception to this is Nullable<T> when used with elements, for example:

[XmlElement("job")]
public int? Job { get; set; }

Might result in:

<user ...>
    <job xsi:nil="true" />
</user>

Which is again very different to your example xml. In the general case, it is possible to control serialization using a number of methods:

• the IsNullable property of [XmlElement]
• adding a [DefaultValue]
• adding a public bool ShouldSerialize{propname}() {...} method
• adding a [XmlIgnore] public bool {propname}Specified {get {...} set {...}} property

However; without a repeatable example to run your example against, it is impossible to answer fully.

---

Re the updated question; this should accomplish that, but it isn't clear what these other properties are (that you want to not show if null).

[Serializable, XmlRoot("user")]
public partial class User
{
    [XmlAttribute("id")]
    public int Id {get;set;} // snipped more complex property implementation
    [XmlAttribute("name")]
    public string Username  {get;set;} // ditto
}

Answer 4

Are you sure

 GetColumnValue<string>("Username");

is returning null and not blank? This seems like the most likely explanation...