Question

This is the scenario:

I have nested classes and need to serialize then in an xml document

[XmlRoot(Namespace="http://www.foo.bar/myschema")]
public class root 
{
    [XmlAttribute]
    public string version { get; set; }

    [XmlElement]
    public child child { get; set; }

    ...
}

[XmlRoot(Namespace="http://www.foo.bar/myschema")]
public class child
{
    [XmlElement]
    public int elemA { get; set; }

    [XmlElement]
    public string elemB { get; set; }

    ...
}

I have created an method based in another example to remove additional namespaces and set a custom one:

public static void Save<T>(this T type, string path)
{
    System.Xml.Serialization.XmlSerializer xs = 
        new System.Xml.Serialization.XmlSerializer(type.GetType());

    System.Xml.Serialization.XmlSerializerNamespaces ns = 
        new System.Xml.Serialization.XmlSerializerNamespaces();
    ns.Add("", "http://www.foo.bar/myschema");

    using(XmlWriter file = XmlWriter.Create(path))
    {
        xs.Serialize(file, type, ns);
    }
}

And I get this code as result:

<?xml version="1.0" encoding="utf-8"?>
<root xmlns="http://www.foo.bar/myschema" version="2.00">
    <child>
        <elemA>1</elemA>
        ...
    </child>
</root>

But expected this:

<?xml version="1.0" encoding="utf-8"?>
<root xmlns="http://www.foo.bar/myschema" version="2.00">
    <child xmlns="http://www.foo.bar/myschema">
        <elemA>1</elemA>
        ...
    </child>
</root>

We must set the custom namespace declaration in both tags. Is this possible?

Edit:

Here is a real-world example:

<?xml version="1.0" encoding="UTF-8"?>
<enviNFe xmlns="http://www.portalfiscal.inf.br/nfe" versao="1.01">
    <idLote>200602220000001</idLote>
    <NFe xmlns="http://www.portalfiscal.inf.br/nfe">
        <infNFe Id="NFe31060243816719000108550000000010001234567890" versao="1.01">
        ...
        <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
        ...
    </NFe>
    <NFe xmlns="http://www.portalfiscal.inf.br/nfe">
        <infNFe Id="NFe31060243816719000108550000000010011234567900" versao="1.01">
        ...
        <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
        ...
    </NFe>
    <NFe xmlns="http://www.portalfiscal.inf.br/nfe">
        <infNFe Id="NFe31060243816719000108550000000010021234567916" versao="1.01">
        ...
        <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
        ...
    </NFe>
</enviNFe>

Answer 1

From an XML point of view your examples are identical, so the first one is perfectly fine. If you have to use the second one, there is a serious problem with our XML understanding or your processing pipeline.