List vs Set vs Bag in NHibernate

Question

What's the difference between a list, set and bag in the NHibernate mapping file? How does each relate to the .NET collections?

Answer 1

NHibernate semantics:

1. List: Ordered collection of entities, duplicate allowed. Use a .NET IList in code. The index column will need to be mapped in NHibernate.

2. Set: Unordered collection of unique entities, duplicates not allowed. Use Iesi.Collection.ISet in code (NH prior to v4) or System.Collections.Generic.ISet (NH v4+). It is important to override GetHashCode and Equals to indicate the business definition of duplicate. Can be sorted by defining an orderby or by defining a comparer resulting in a SortedSet result.

3. Bag: Unordered list of entities, duplicates allowed. Use a .NET ICollection<T> in code. The index column of the list is not mapped and not honored by NHibernate.