Why did .NET set a default attribute value?

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Scott Liu - 23 Sep 2004 23:47 GMT

HI, All,

I have a web service doing a string search. It has an operator and a
searchValue field. The operator is defined as an attribute and required. The
xml is as below.

    
    <simpleType name="SearchStringFieldOperator">
        <restriction base="xsd:string">
            <enumeration value="is"/>
            <enumeration value="isNot"/>
        </restriction>
    </simpleType>
    <complexType name="SearchStringField">
        <sequence>
            <element name="searchValue" type="xsd:string"/>
        </sequence>
        <attribute name="operator" type="SearchStringFieldOperator" use="required"/>
    </complexType>

It works when I explicitly set the operator attribute since it is required.
One interesting problem I found is that when the operator is not set in my
.NET (c#) web service client the .NET studio sets a default value of “is” to
the operator. Since I do not have a default value chosen in my object
definition I do not see why .NET picks up one for me.

Included: c# references.cs

/// <remarks/>
[System.Xml.Serialization.XmlTypeAttribute(Namespace="urn:mynamespace")]
public class SearchStringField {

/// <remarks/>
public string searchValue;

/// <remarks/>
[System.Xml.Serialization.XmlAttributeAttribute()]
public SearchStringFieldOperator @operator;
}

/// <remarks/>
[System.Xml.Serialization.XmlTypeAttribute(Namespace="urn:mynamespace")]
public enum SearchStringFieldOperator {

/// <remarks/>
@is,

/// <remarks/>
isNot,
}

Any help is appreciated greatly,

Thanks,

Scott

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Derek Harmon - 27 Sep 2004 01:17 GMT

> One interesting problem I found is that when the operator is not set in my
> .NET (c#) web service client the .NET studio sets a default value of "is" to
[quoted text clipped - 7 lines]
> isNot,
> }

When an Enum is defined without explicit values, then .NET assigns
values starting with 0 and increasing. So the above declaration is
actually equivalent to,

public enum SearchStringFieldOperator {
@is = 0,
isNot = 1,
}

Enums are represented as integers, and the field @operator you have
is of the SearchStringFieldOperator enum type, too. Since enums are
really integers, this field is initialized to 0, which is the same integer
value as the first enum literal in the above declaration, @is. This is
why when the Framework constructs a default SearchStringField the
@operator field already has the default value, @is.

If you want to avoid this behavior, then I'd try changing the definition
of the SearchStringFieldOperator enum.

public enum SearchStringFieldOperator {
@is = 1,
isNot,
}

This way, none of the literals of SearchStringFieldOperator correspond
to zero, which your enum fields will be initialized to by default.

Derek Harmon

Reply to this Message

Scott Liu - 28 Sep 2004 08:33 GMT

Thanks, Derek. This explains it.

The field definition is generated by .NET framework thus I do not want to
change it. The other solution then is to add a dummy field "notSet" as the 0
th enum value or to choose a default value explicitly in the schema.

Scott

> > One interesting problem I found is that when the operator is not set in my
> > .NET (c#) web service client the .NET studio sets a default value of "is" to
[quoted text clipped - 36 lines]
>
> Derek Harmon

Reply to this Message

Scott Liu - 28 Sep 2004 21:09 GMT

On second thought is there a preference in .NET which I can set to instruct
it to ignore providing a default value?

Thanks,

Scott

> Thanks, Derek. This explains it.
>
[quoted text clipped - 44 lines]
> >
> > Derek Harmon

Reply to this Message

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Why did .NET set a default attribute value?

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