NHibernate Fluent Join mapping for many to one relationship - nhibernate

Question

I'm trying to fetch a collection of read-only objects from NHibernate where all the properties come from a single table (Answers), with the exception of one property that comes from another table (Questions) in a many to one relationship. The fact it's two tables is an implementation detail that I want to hide, so I want the repository to return a sensible aggregate. The trouble is this requires I have two classes, one for each table, that NHibernate returns and then I have to select/map that into a third class that my repository returns. This feels a bit rubbish so instead I was hoping to have a mapping that joins the two tables for me but maps all the columns onto a single class. My mapping looks like this:
public QuestionAnswerMap()
{
ReadOnly();
Table("Question");
Id(x => x.Id).Column("questionId").GeneratedBy.Identity();
Map(x => x.AnswerShortCode).Column("AnswerShortCode");
Join("Answers", join =>
{
join.Fetch.Join();
join.KeyColumn("questionId").Inverse();
join.Map(x => x.QuestionId).Column("QuestionId");
join.Map(x => x.AnswerId).Column("AnswerId");
join.Map(x => x.MemberId).Column("MemberId");
});
}
The SQL this generates looks perfect and returns exactly what I want, but when there are multiple Answers that join to the same row in the Questions table, NHibernate seems to map them to objects wrongly - I get the right number of results, but all the Answers that have a common Question are hydrated with the first row in sql result for that Question.
Am I doing this the right way? NH is generating the right SQL, so why is it building my objects wrong?

Answer 1

because Join was meant to be this way. It assumes a one to one association between the two tables which are not the case.
Instead of a mapped Entity i would prefere a on the fly Dto for this:
var query = session.Query<Answer>()
.Where(answer => ...)
.Select(answer => new QuestionAnswer
{
QuestionId = answer.Question.Id,
AnswerShortCode = answer.Question.AnswerShortCode,
AnswerId = answer.Id,
MemberId = answer.MemberId,
});
return query.ToList();