设置nillable = true并在XML文档中使用默认属性是否有效？

Question

Using C# and .Net 4.0

I have a generated schema that looks like this:

<xsd:element name="EstimatedDate" minOccurs="0" nillable="true" default="1900-01-01T00:00:00">
  <xsd:complexType>
       <xsd:simpleContent>
           <xsd:extension base="xsd:dateTime">
                <xsd:attribute name="origVal" type="xsd:dateTime" use="optional" />
           </xsd:extension>
       </xsd:simpleContent>
  </xsd:complexType>

When I serialize the object with a null value I get:

<EstimatedDate xsi:nil="true" />

But I am getting a deserialization: "There must be no fixed value when an attribute is 'xsi:nil' and has a value of 'true'."

When I look at the XML specification I do not see that nillable and default properties are mutually exclusive, but my other dateTime XML types that are nillable but do not have a default property work correctly.

Answer 1

I think that maybe it is one of those confusing areas in the XML Schema specification (interesting enough, even 1.1 spec is only dissalowing default and fixed combination); if you consider that default values for elements apply when the elements are present and empty , and that nilled elements must not have any content, then it kind of make sense to get confused... which one is it: null or default? In other words, when both conditions are present, which one takes precedence? I guess the deserializer is kind of asking for help there...

Answer 2

The error message describes a constraint that is present in the spec: Validation Rule: Element Locally Valid (Element) clause 3.3.2 says that when xsi:nil=true, there must be no fixed value. However, there is no ban on a default value, as far as I can see, so it seems your schema processor is over-eager to find fault.

I think the correct behavior for your schema is: if the element is empty and xsi:nil is absent or false, use the default value; if the element is empty and xsi:nil is true, leave it as is.

(you can try getting Microsoft to fix this, or you can try switching to Saxon...)