return NS_ERROR_ALREADY_INITIALIZED;
mDB->RemoveObserver(this);
RDFXULBuilderImpl::SetDataBase(nsIRDFCompositeDataSource* aDataBase){    NS_PRECONDITION(aDataBase != nsnull, "null ptr");    if (! aDataBase)        return NS_ERROR_NULL_POINTER;    NS_PRECONDITION(mDB == nsnull, "already initialized");    if (mDB)        return NS_ERROR_ALREADY_INITIALIZED;    mDB = dont_QueryInterface(aDataBase);    mDB->AddObserver(this);    return NS_OK;}