how to flatten a model with NHibernate - nhibernate

Question

Say I have three tables Products, Languages and ProductTranslations that look like the following:
(1) ProductId
(1) StandardName
(1) Price
(2) LanguageId
(2) LanguageName
and
(3) ProductTranslationId
(3) ProductId
(3) LanguageId
(3) LocalName
(3) LocalDescription
In my object model, I need a single object (single class map) that contains the following
(3) ProductTranslationId
(2) Language
(3) LocalName
(3) LocalDescription
(1) Price
This object is only used for display, so read-only (immutable) is fine.
ProductTranslationId uniquely identifies a row.
If necessary, this object can include the LanguageID and ProductID values as well. the important feature is that this needs to include the Language and Price values from the ONE side of this one to many relationship.
I can see how to do this in 3 separate classes using Many-to-One, but how can I do this with one class, where ProductTranslationId is the <id> value?
Is there an alternative that does not require creating a view in the database?

Answer 1

Option 1
// FluentNHibernate Mapping
public class ProductTranslationDtoMap : ClassMap<ProductTranslationDto>
{
public ProductTranslationDtoMap()
{
ReadOnly();
Table(" ProductTranslation");
Id(x => x.Id, "ProductTranslationId");
Map(x => x.Language).Formula("(SELECT l.LanguageName FROM Language l WHERE l.LanguageId = LanguageId)"); // simple and highly portable sql formula
Map(x => x.LocalName);
Map(x => x.LocalDescription);
Map(x => x.Price).Formula("(SELECT p.Price FROM Products p WHERE p.ProductId = ProductId)");
}
}
Option 2
Product prod = null;
Language lang = null;
TranslationDto alias = null;
var results = session.QueryOver<ProductTranslation>()
.JoinAlias(pt => pt.Language, () => lang)
.JoinAlias(pt => pt.Product, () => prod)
.SelectList(list => list
.Select(pt => pt.Id).WithAlias(() => alias.ProductTranslationId)
.Select(() => lang.Name).WithAlias(() => alias.Language)
...)
.TransformUsing(Transformers.AliasToBean<TranslationDto>())
.List<TranslationDto>();

Answer 2

Instead of using a NHibernate mapping you could also use a class mapper like AutoMapper to create a flat representation of your complex object graph. The advantage would be one nhibernate mapping less to maintain (although the fluent variant from Firo offers compiler syntax checking) in case your db schema changes. The disadvantage of course would be speed, as you first have to make nhibernate create your complex object graph, then transform that graph into a flat object. If you only need this one flat object, you may be better of with a single NH mapping. If you think about creating several more views, a class mapper might be worth a look.