I have two NHibernate entities with a one-to-one relationship. Let's call them Dog and Owner.
public class Dog { public virtual int Id { get;set; } public virtual Owner Owner { get; set; } } public class Owner { public virtual int Id { get; set; } public virtual Dog Dog { get; set; } } And Dog may have one or zero owners. The Fluent/NHibernate mappings are as so:
public class DogMap : ClassMap<Dog> { public DogMap() { Table("Dogs"); Id(x => x.Id); HasOne( x=> x.Owner) .Fetch.Join() .Not.LazyLoad(); } } public class OwnerMap : ClassMap<Owner> { public OwnerMap() { Table("Owners"); // Owners share the same primary-key as dogs Id(x => x.Id).GeneratedBy.Foreign("Dog"); References( x => x.Dog) .Unique() .Not.LazyLoad(); } } Now I simply wish to select Dogs which don't have an Owner.
I assumed the query would be:
Owner owner = null; var ownerlessDogs = session .QueryOver<Dog>() .Left.JoinAlias(x => x.Owner, () => owner) // Restrict on alias .WhereRestrictionOn(() => owner).IsNull .List(); But as you may have guessed, this does not work. It throws 'Object reference not set to ...'.
If I try,
var ownerlessDogs = session .QueryOver<Dog>() .Left.JoinAlias(x => x.Owner, () => owner) // Restrict on property of root object .WhereRestrictionOn(x => x.Owner).IsNull .List(); It generates basically generates
SELECT {{relevant columns}} FROM Dogs dogs LEFT OUTER JOIN OWNERS owners WHERE dogs.Id IS NULL Almost right, but it is filtering on the primary-key of dogs, rather than the dogs foreign-key on owners.
