Question

Really quick question..

Does Linq2NHibernate always create a left join to retrieve relationships? Is there a way that I can get an inner one instead?

Thank you in advance.

Filipe

Answer 1

As far as I know.

For any relationship that is not One-to-One, NHibernate makes the assumption that the relationship could have 0 to many results, thus uses a Left Join.

I don’t know about Linq2NHibernate, but in NH3 using QueryOver API you can specify the join types.

For example, give a Product with a Category. If you wrote:

var result = Session.QueryOver<Product>()
                    .Fetch(x => x.Category).Eager
                    .List();

This will result in a left join, if you wanted to specify an inner join you could write the same query as:

var result = Session.QueryOver<Product>()
                    .JoinQueryOver(x => x.Category, JoinType.InnerJoin)
                    .List();

This will result in an Inner Join.

As far as I know you can’t specify join types when using the LINQ provider (Query<T> in NH3)