How do you prevent null elements from being serialized?

[Kenny Mullican]

I am using complex types in order to support serialization/deserialization
of floating point numbers, since floating points can't be null.
I've seen how to suppress attributes that are "not specified", such as
having a float member called Value, and a bool member called ValueSpecified.
This instructs the XML Serializer to omit that attribute altogether if it
wasn't "Specified" . But how can I tell it to omit the XML element
altogether?
Here's the problem:
I deserialize an object that looks like this:
<person>

<name>Joe</name>

<age>37</age>

</person>

When deserialized, I get an object of type person, with a field age of type
floatType which has Value = 37 and ValueSpecified = false.
If I change name to "Bob" (p.name = "Bob"), and then immediately serialize
that object to XML, I get:
<person>

<name>Bob</name>

<age />

</person>

This indicates that age should now be null (if I pass this off to a SOAP
server for instance), or if that value is not allowed to be nulled, then I
get a SOAP exception.
If I explicitly set p.age.ValueSpec ified = true or set p.age.Value = 36
(which implicitly sets ValueSpecified to true)
Then I get the expected
<person>

<name>Bob</name>

<age>36</age>

</person>

What I would like to see happen is if ValueSpecified is false, then just
leave that element off altogether. Is there a way to do this?
Thanks for your help

Kenny

[Dino Chiesa [Microsoft]]

Kenny, you don't show your code, but something fishy is going on.

1. De-serializing from

<person>
<name>Joe</name>
<age>37</age>
</person>

....I get name=Joe, Age=37 and AgeSpecified = true (not false as you report).

Also, changing the Name from Joe to Bob should not affect Age or
AgeSpecified, as you report. Also, changing Age does not directly affect
AgeSpecified. These things are true, unless you have put some non-default
handling in the property getter/setter.

What I would like to see happen is if ValueSpecified is false, then just
leave that element off altogether. Is there a way to do this?
This is the default behavior?, so I don't understand why you are asking
this. The code enclosed below demonstrates this, and some other interesting
things in XML serialization.

In fact you have to do something special in order to get an empty element
(eg "<Age />") to appear in an XML stream output from the .NET XML
Serializer. If you use isnullable:=Tru e in the XmlElementAttri bute, you
will get <Age xsi:nil="true" />, which is not quite the same thing.
-Dino


----- Begin Code -----
// XmlIgnoreTest.c s
//
// Exercises some of the XmlIgnore stuff
//
// compile with:
//
// (c) Ionic Shade
// Wed, 17 Nov 2004 10:02
//

using System.IO;
using System.Xml.Seri alization;
// This is the default class generated from xsd.exe
[System.Xml.Seri alization.XmlRo otAttribute(Nam espace="", IsNullable=fals e)]
public class Person {

[System.Xml.Seri alization.XmlEl ementAttribute( Form=System.Xml .Schema.XmlSche maForm.Unqualif ied)]
public string Name;

[System.Xml.Seri alization.XmlEl ementAttribute( Form=System.Xml .Schema.XmlSche maForm.Unqualif ied)]
public System.Single Age;

[System.Xml.Seri alization.XmlIg noreAttribute()]
public bool AgeSpecified;
}


namespace Ionic {

public class XmlTextWriterFo rmattedNoDeclar ation :
System.Xml.XmlT extWriter {
public XmlTextWriterFo rmattedNoDeclar ation (System.IO.Text Writer w) :
base(w) { Formatting= System.Xml.Form atting.Indented ;}
public override void WriteStartDocum ent () { }
}
public class TestDriver {

static void Main(string[] args) {

try {

string OriginalXml=
"<Person>\n " +
" <Name>Joe</Name>\n" +
" <Age>37</Age>\n" +
"</Person>\n" +
"";

System.Console. WriteLine("\n== =============== =============== ============\nO riginal
XML:\n"+ OriginalXml);

XmlSerializer s1 = new XmlSerializer(t ypeof(Person));
Person p= null;
using (System.IO.Stri ngReader sr= new
System.IO.Strin gReader(Origina lXml)) {
p = (Person) s1.Deserialize( sr);
}

// suppress default namespace entries in the root elt
XmlSerializerNa mespaces ns = new XmlSerializerNa mespaces();
ns.Add( "", "" );

// use a custom TextWriter to suppress the XML declaration

System.Console. WriteLine("\n== =============== =============== ============\nO riginal
values:");
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;

System.Console. WriteLine("\n== =============== =============== ============\nC hanging
the name does not change the age:");
p.Name= "Bob";
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;
System.Console. WriteLine("\n== =============== =============== ============\nU n-specifying
the Age results in this:");
p.AgeSpecified= false;
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;
string OriginalXml2=
"<Person>\n " +
" <Name>Shirley </Name>\n" +
" <Age />\n" +
"</Person>\n" +
"";
System.Console. WriteLine("\n== =============== =============== ============\nC ase
2: Original XML:\n"+ OriginalXml2);
p=null;
try {
System.Console. WriteLine("\n(D e-serializing from this will
fail...)\n");
using (System.IO.Stri ngReader sr= new
System.IO.Strin gReader(Origina lXml2)) {
p = (Person) s1.Deserialize( sr);
}
}
catch (System.Invalid OperationExcept ion ex1) {
System.Console. WriteLine("As Expected, an Exception was generated:
" + ex1);

}

if (p!= null) {
System.Console. WriteLine("\n== =============== =============== ============\nO riginal
values:");
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;
}

p= new Person();
p.Name= "Henry";
System.Console. WriteLine("\n== =============== =============== ============\nN ew
Instance, setting only Name:");
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;

p.Age= 66;
System.Console. WriteLine("\n== =============== =============== ============\na lso
setting Ageon that instance:");
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;

p.AgeSpecified= true;
System.Console. WriteLine("\n== =============== =============== ============\na nd
now setting AgeSpecified:") ;
s1.Serialize(ne w
XmlTextWriterFo rmattedNoDeclar ation(System.Co nsole.Out), p, ns);
System.Console. WriteLine("\n") ;

}
catch (System.Excepti on e1) {
System.Console. WriteLine("Exce ption!\n" + e1);
}
}
}
}

----- End Code -----
"Kenny Mullican" <no***********@ nowayemonarch.n et> wrote in message
news:%2******** **********@TK2M SFTNGP11.phx.gb l...I am using complex types in order to support serialization/deserialization
of floating point numbers, since floating points can't be null.
I've seen how to suppress attributes that are "not specified", such as
having a float member called Value, and a bool member called
ValueSpecified. This instructs the XML Serializer to omit that attribute
altogether if it wasn't "Specified" . But how can I tell it to omit the
XML element altogether?
Here's the problem:
I deserialize an object that looks like this:
<person>

<name>Joe</name>

<age>37</age>

</person>

When deserialized, I get an object of type person, with a field age of
type floatType which has Value = 37 and ValueSpecified = false.
If I change name to "Bob" (p.name = "Bob"), and then immediately serialize
that object to XML, I get:
<person>

<name>Bob</name>

<age />

</person>

This indicates that age should now be null (if I pass this off to a SOAP
server for instance), or if that value is not allowed to be nulled, then I
get a SOAP exception.
If I explicitly set p.age.ValueSpec ified = true or set p.age.Value = 36
(which implicitly sets ValueSpecified to true)
Then I get the expected
<person>

<name>Bob</name>

<age>36</age>

</person>

What I would like to see happen is if ValueSpecified is false, then just
leave that element off altogether. Is there a way to do this?
Thanks for your help

Kenny