One-To-One Nhibernate invokes multiple SQL statements

Question

I have classes with a one-to-one circular reference and suppose they look something like this.

public class Foo
{
    public Bar Bar { get; set; }

    /* Some irrelevant code */
}

and

public class Bar
{
    public Foo Foo { get; set; }

    /* Some irrelevant code */
}

and a fluent nhibernate map

BarMap
{
    Table("Bars");
    // Some mappings
    Reference(x => x.Foo).Column("FooId");
}

FooMap
{
    Table("Foos");
    // Some Mappings
    HasOne(x => x.Bar).PropertyRef(x => x.Foo).Not.Lazy.Cascade.SaveUpdates();
}

I realize you can't lazily load a one-to-one relationship in nhibernate so what I want to do is to select all of the entirety of Bars and join it to Foo when I want something from Foo. I figured I need to fetch Bar but when I execute:

var foos = session.Query<Foo>().Where(/*Some boolean logic*/).Fetch(x => x.Bar).ToList();

Nhibernates then executes multiple SQL statements, selecting one Bar for each Foo. I want to only select twice. Once for Foo and once for Bar - since this can't be lazy-loaded. How can I make this happen?

Answer 1

My problem was that I Bar had another circular reference to another object, say Baz:

BarMap
{
    Table("Bars");
    Reference(x => x.Foo).Column("FooId");
    HasOne(x => x.Bar).PropertyRef(x => x.Bar).Not.Lazy.Cascade.SaveUpdates();
}

BazMap
{
    Table("Baz");
    Reference(x => x.Foo).Column("BarId");
}

So I solved the problem by joining Foo, Bar and Baz.

var Foos = session
    .Query<Foo>()
    .Fetch(x => x.Bar)
    .ThenFetch(x => x.Baz)
    .ToList();

Sort of over the top when considering I only really needed a few fields in the Foos table.

Answer 2

You might be able to use futures to accomplish what you want. For example:

session.Query<Bar>().Fetch(x => x.Foo).ToFuture();
var foos = session.Query<Foo>().Where(/*Some boolean logic*/).Fetch(x => x.Bar).ToList();

The idea is that using ToFuture() on the first query will ensure that both queries run simultaneously, and nhibernate may use the results of the first query to help populate the second query. You may need to play around with the actual queries to get things working the way you expect.