Is it possible for a wrapped object to "become" an object of the same type?

I have a wrapped XmlDocument class, and in it, I'd like to check to see if there's a cached XmlDocument object with the same name, and then "become" that object. Is there a better way to do this?

namespace myXmlUtilities {
  class SpecificAutoLoadingCmsXmlDocument :开发者_JAVA技巧 System.Xml.XmlDocument {
    private string documentName = "joiseyMike.xml";

    public void loadFromCms() {
        if (cache[documentName] != null) 
            LoadXml(((XmlDocument)cache[documentName]).OuterXml);
        else
            // ... load from the CMS's database.
    }

    public SpecificAutoLoadingCmsXmlDocument() {
        loadFromCms();
    }
  }

Edited: I made the example a little more true-to life. Apologies for the earlier quick-and-dirty version.

You should use a factory pattern instead which would allow you to put this logic into the factory method(s).

So you'd end up with:

public static XmlDocument GetNewDocument(string documentName) {
    if (cache[documentName] != null) 
        return cache[documentName];
    else
        return new XmlDocument();
}

So instead of doing a simple new XmlDocument();, you'd make a call to the static GetNewDocument() method.

I would rework the arch here. You are missing a seperation of concerns. Why not use a factory to check if the cache has that name and give you that object back? An object trying to construct itself seems messy to me.