I have a c# class that has 20+ string properties. I set about a fourth of those to an actual value. I would like to serialize the class and get an output of
<EmptyAttribute></EmptyAttribute>
for a property
public string EmptyAttribute {get;set;}
I do not want the output to be
<EmptyAttribute xsi:nil="true"></EmptyAttribute>
I am using the following class
public class XmlTextWriterFull : XmlTextWriter
{
public XmlTextWriterFull(string filename) : base(filename,Encoding.UTF8) { }
public override void WriteEndElement()
{
base.WriteFullEndElement();
base.WriteRaw(Environment.NewLine);
}
}
so that I can get the full tags. I just don't know how to get rid of the xsi:nil.
Synopsis. The xsi:nil attribute indicates that a certain element does not have a value or that the value is unknown. This is not the same as having a value that is zero or the empty string. Semantically, it is equivalent to SQL's null.
If an element has the xsi:nil attribute specified, it indicates that the element is present but has no value, and therefore no content is associated with it. If an XML schema has defined the nillable attribute as true, it is mapped as a required attribute that takes a Boolean value.
The way to have the XmlSerializer
serialize a property without adding the xsi:nil="true"
attribute is shown below:
[XmlRoot("MyClassWithNullableProp", Namespace="urn:myNamespace", IsNullable = false)]
public class MyClassWithNullableProp
{
public MyClassWithNullableProp( )
{
this._namespaces = new XmlSerializerNamespaces(new XmlQualifiedName[] {
new XmlQualifiedName(string.Empty, "urn:myNamespace") // Default Namespace
});
}
[XmlElement("Property1", Namespace="urn:myNamespace", IsNullable = false)]
public string Property1
{
get
{
// To make sure that no element is generated, even when the value of the
// property is an empty string, return null.
return string.IsNullOrEmpty(this._property1) ? null : this._property1;
}
set { this._property1 = value; }
}
private string _property1;
// To do the same for value types, you need a "helper property, as demonstrated below.
// First, the regular property.
[XmlIgnore] // The serializer won't serialize this property properly.
public int? MyNullableInt
{
get { return this._myNullableInt; }
set { this._myNullableInt = value; }
}
private int? _myNullableInt;
// And now the helper property that the serializer will use to serialize it.
[XmlElement("MyNullableInt", Namespace="urn:myNamespace", IsNullable = false)]
public string XmlMyNullableInt
{
get
{
return this._myNullableInt.HasValue?
this._myNullableInt.Value.ToString() : null;
}
set { this._myNullableInt = int.Parse(value); } // You should do more error checking...
}
// Now, a string property where you want an empty element to be displayed, but no
// xsi:nil.
[XmlElement("MyEmptyString", Namespace="urn:myNamespace", IsNullable = false)]
public string MyEmptyString
{
get
{
return string.IsNullOrEmpty(this._myEmptyString)?
string.Empty : this._myEmptyString;
}
set { this._myEmptyString = value; }
}
private string _myEmptyString;
// Now, a value type property for which you want an empty tag, and not, say, 0, or
// whatever default value the framework gives the type.
[XmlIgnore]
public float? MyEmptyNullableFloat
{
get { return this._myEmptyNullableFloat; }
set { this._myEmptyNullableFloat = value; }
}
private float? _myEmptyNullableFloat;
// The helper property for serialization.
public string XmlMyEmptyNullableFloat
{
get
{
return this._myEmptyNullableFloat.HasValue ?
this._myEmptyNullableFloat.Value.ToString() : string.Empty;
}
set
{
if (!string.IsNullOrEmpty(value))
this._myEmptyNullableFloat = float.Parse(value);
}
}
[XmlNamespaceDeclarations]
public XmlSerializerNamespaces Namespaces
{
get { return this._namespaces; }
}
private XmlSerializerNamespaces _namespaces;
}
Now, instantiate this class and serialize it.
// I just wanted to show explicitly setting all the properties to null...
MyClassWithNullableProp myClass = new MyClassWithNullableProp( ) {
Property1 = null,
MyNullableInt = null,
MyEmptyString = null,
MyEmptyNullableFloat = null
};
// Serialize it.
// You'll need to setup some backing store for the text writer below...
// a file, memory stream, something...
XmlTextWriter writer = XmlTextWriter(...) // Instantiate a text writer.
XmlSerializer xs = new XmlSerializer(typeof(MyClassWithNullableProp),
new XmlRootAttribute("MyClassWithNullableProp") {
Namespace="urn:myNamespace",
IsNullable = false
}
);
xs.Serialize(writer, myClass, myClass.Namespaces);
After retrieving the contents of the XmlTextWriter
, you should have the following output:
<MyClassWithNullableProp>
<MyEmptyString />
<MyEmptyNullableFloat />
</MyClassWithNullableProp>
I hope this clearly demonstrates how the built-in .NET Framework XmlSerializer
can be used to serialize properties to an empty element, even when the property value is null (or some other value you don't want to serialize). In addition, I have shown how you can make sure that null
properties are not serialized at all. One thing to note, if you apply an XmlElementAttribute
and set the IsNullable
property of that attribute to true
, then that property will serialize with the xsi:nil
attribute when the property is null
(unless overriden somewhere else).
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