public class Document : EntityBase<Document>
{
    public virtual string Number { get; set; }
    public virtual IList<DocumentDetail> Detail { get; set; }
}
 public class Document : EntityBase<Document>
{
    public virtual string Number { get; set; }
    public virtual IList<DocumentDetail> Detail { get; set; }
}
     public class DocumentMapping : FluentNHibernate.Mapping.ClassMap<Cradle.DomainEntities.Document>
{
    public DocumentMapping()
    {
        Id(x => x.ID);
        Map(x => x.Number).CustomSqlType("varchar(30)").Not.Nullable().Unique();
    }
}        public class DocumentDetailMapping : FluentNHibernate.Mapping.ClassMap<Cradle.DomainEntities.DocumentDetail>
{
    public DocumentDetailMapping()
    {
        Id(x => x.ID);
        Map(x => x.LineNumber).CustomSqlType("varchar(10)"); //this must be unique per document
        References(x => x.Document).Not.LazyLoad();
    }
}