NHibernate中的QueryOver,子节点为nullable

解决方案可能是这样的:

// these will server as fully-type representatives, and aliases
Shop shop = null;
City city = null;
MyDTO dto = null;

// shop query
var query = session.QueryOver<Shop>(() => shop);
// if needed a reference to criteria of the city
var cityPart = query.JoinQueryOver(() => shop.City // reference
    , () => city // alias
    , JoinType.LeftOuterJoin); // left join

// SELECT Clause
query.SelectList(list => list
    .Select(() => shop.Id)
        .WithAlias(() => dto.Id)
    .Select(() => shop.Name)
        .WithAlias(() => dto.Name)

    // Conditional here
    .Select(Projections.Conditional(
                Restrictions.Where(() => city.NameES== null),
                Projections.Constant("---", NHibernateUtil.String),
                Projections.Property(() => city.NameES)
        ))
        .WithAlias(() => dto.NameEs)
    );

var result = query
    .TransformUsing(Transformers.AliasToBean<MyDTO>())
    .List<MyDTO>();