Supoved

Banners - линк на IQueryable бд
Banner - класс объектов из таблички Banners
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XmlSerializer xsSubmit = new XmlSerializer(typeof(List<Banner>));
var subReq = Banners.ToList();

StringWriter sww = new StringWriter();
XmlWriter writer = XmlWriter.Create(sww);
xsSubmit.Serialize(writer, subReq);
var xml = sww.ToString().Dump();