fluent nhibernate mapping with not null foreign key (HasMany)

Question

I have the following mapping in nhibernate. When I call Session.Merge(myparent) I get the an error on the insert indicating that NULL cannot be inserted into the foreign key ( ParentItemId ) column.

How can I adjust the mapping so that the parent key is inserted on insert. If I make the foreign key nullable this mapping works, but two separate statements are issued to the database.

This relationship is a one to many without a reference back to the parent on the child class.

The child class has no parent property.

The child is dependent on the parent.

 HasMany(map => map.Children).Table("ChilrenTable") .KeyColumn("ParentItemId") // this is not nullable. .Cascade .AllDeleteOrphan();

example update

// entity here is the parent instance, which contains the list // of children. using (var tx = Session.BeginTransaction()) { entity = Session.Merge(entity); // this line causes the problem. Session.SaveOrUpdate(entity); Session.Flush(); tx.Commit(); return entity; }

Answer 1

Inverse Attribute in NHibernate

HasMany(map => map.Children).Table("ChilrenTable")
   .KeyColumn("ParentId") // this is not nullable.
   .Inverse()  // <--- This is the key here
   .Cascade
   .AllDeleteOrphan();