adding Xml attributes to objects serialized from .NET

I have a class called CustomerDetails, and I manage these objects in a System.Collections.Generic.List(Of CustomerDetails). I serialize this object in an ordinary way...

    Private Sub CustomerDetailsExportToXml(Details As System.Collections.Generic.List(Of CustomerDetails))
        Dim x As New System.Xml.Serialization.XmlSerializer(Details.GetType)
        Using s As New FileStream("customerdetails.xml", FileMode.Create)
        x.Serialize(s, Details)
        End Using
    End Sub

...and get ordinary Xml...

  <?xml version="1.0"?>
  <ArrayOfCustomerDetails xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <CustomerDetails>
      <Acronym>MSD</Acronym>
      <FriendlyName>Main Street Diner</FriendlyName>
    </CustomerDetails>
  </ArrayOfCustomerDetails>

To aid readability, I want to add an attribute to the CustomerDetails tag called "Acronym" that would contain the value of the <Acronym> tag:

<CustomerDetails Acronym="MSD">

I can do this in a post-serialization method where I load/modify/save the Xml, but I'm afraid of the resulting Xml not being de-serializable. Can the addition of the attribute be done at time of serialization?

Since you already seem to have Acronym with the same value as an element, this should be pretty simple to get the serializer to do for you. Presumably right now you have something like:

public class CustomerDetails
{
    public string Acronym {get;set;}
}

To make that an attribute instead, all you have to do is ask:

public class CustomerDetails
{
    [XmlAttribute]
    public string Acronym {get;set;}
}

You can also do this without attributes by configuring the serializer manually, but it is a lot more work.

Update

Marc Gravell's answer is much more concise and keeps it so it can be deserialized easily too.

Here is a fiddle using the XmlAttribute decorator: https://dotnetfiddle.net/6T0U4d

Original Answer

> I can do this in a post-serialization method where I load/modify/save the Xml, but I'm afraid of the resulting Xml not being de-serializable. Can the addition of the attribute be done at time of serialization?

That is correct. If you mess with the serialization output then it is unlikely that it will be deserializable.

However, what you're asking can be done pretty easily by following these steps:

1. Instead of using a FileStream you can use a StringWriter to get the output as an in-memory string
2. Take the XML literal and load it into an XDocument
3. Loop over the CustomerDetails elements in the ArrayOfCustomerDetails element
4. Set the attribute value to the Acronym element value
5. Remove the Acronym element
6. Save the XDocument XML to your file

For example:

Dim serializer = New XmlSerializer(details.GetType())
Dim xmlLiteral = String.Empty
Using writer = New StringWriter()
	serializer.Serialize(writer, details)
	xmlLiteral = writer.ToString()
End Using

Dim detailsXmlDocument = XDocument.Parse(xmlLiteral)
For Each customerDetailsElement In detailsXmlDocument.Element("ArrayOfCustomerDetails").Elements("CustomerDetails")
	customerDetailsElement.SetAttributeValue("Acronym", customerDetailsElement.Element("Acronym").Value)
	customerDetailsElement.Element("Acronym").Remove()
Next

IO.File.WriteAllText("customerdetails.xml", detailsXmlDocument.ToString())

Fiddle: https://dotnetfiddle.net/kAz5Ol

You could get the deserialization to work by just reversing the process.