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XSD how to specify null in enum

For XSD definition, how can null be included as enum for a field defined as string?

Is this correct: <xs:enumeration value="null"/>

<xs:element name="status_color" nillable="true">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="G"/>
<xs:enumeration value="R"/>
<xs:enumeration value="Y"/>
<xs:enumeration value="null"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

I'm using xsd.exe /xsd2code.exe and it turns the code into this: @null

[System.CodeDom.Compiler.GeneratedCodeAttribute("Xsd2Code", "3.3.0.31927")]
[System.SerializableAttribute()]
[System.Xml.Serialization.XmlTypeAttribute(AnonymousType=true, Namespace="http://pmve.web.boeing.com/action_item_dtl_in")]
public enum status_color {
G,
R,
Y,
@null,
}

kaufmed

Enums in C# are value types--hence they cannot take a value of null. As far as the "@null", "null" is a reserved word in C#. Because of this, the "@" was pre-pended to it. You can use any reserved word as an identifier in C# if you preface it with an "at" symbol.

E.g.

@int
@struct
@class

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kaufmed

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nicholsf

ASKER

What about xsd and is this valid for defining null:

<xs:enumeration value="null"/>

I think it is but I'm not a 100%

Note: I realize that nillable="true" for the element will work. but if you want a list of valid enum values.

kaufmed

I don't have access to my copy of XMLSpy ATM; the best I can offer right now would be to try empty string for nil:

<xs:enumeration value=""/>

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kaufmed

It seems to me, however, that having a value of nil defeats the purpose of having an enumeration. An enumeration is a way of saying: "This item MUST be one of these values." A value of nil seems counter-intuitive to me.

nicholsf

ASKER

Many thanks for providing the info on the @ in C#.
That was helpful..increased my knowledge of C#.