Question

Simple question: does it matter which side of a bidirectional many-to-many relationship you set as the inverse in NHibernate? And if so, what are the implications of setting it on one end vs. the other?

Some more clarification: I’m setting both sides of the relationship:

Parent.Children.Add(child);
Child.Parents.Add(parent);

In a case like this, does it matter which side I mark as inverse?

Answer 1

Yes it matters, changes made only to the inverse end of the association are not persisted

You may check nhibernate documentation for further details. Here you have the link:

http://www.nhforge.org/doc/nh/en/#collections-bidirectional

EDIT

My answer doesn’t change with your addition, but I’ll try to explain it better 🙂

if you set Parent.Children with inverse = true you need to save Child object in order to save the relation. If you ONLY save Parent then the relation won’t be saved

if you set Child.Parent with inverse = true you need to save Parent object in order to save the relation. If you ONLY save Child then the relation won’t be saved

category.Items.Add(item);  // The category now "knows" about the relationship
item.Categories.Add(category);  // The item now "knows" about the relationship

session.Update(item);    // No effect, nothing will be saved!
session.Update(category);    // The relationship will be saved