Creating a NHibernate object and initializing a Set

Question

I have a Table called Product and I have the Table StorageHistory.

Now, Product contains a reference to StorageHistory in it's mappings

<set name="StorageHistories" lazy="false">
  <key column="ProductId" />
  <one-to-many class="StorageHistory" />
</set>

And it works, when I retrieve an object from the ORM I get an empty ISet.

What gives me a headache is how to construct the object in the first place. When I do the following:

var product = new Product();
session.Save(product);

the product.StorageHistories property is NULL and I get a NullReferenceException. So, how do I add items to that collection, or should I go the way to add the StorageHistory items themselves to the DB?

Answer 1

I always do the following in the ctor of the parent object:

histories = new HashedSet();

This covers the Save() use case. The Load()/Get() etc usecase is covered by NHibernate as you stated.

Answer 2

Why not?

private ISet _StorageHistories;
public virtual ISet StorageHistories {
     protected set { _StorageHistories = value;}
     get { if (_StorageHistories == null) _StorageHistories = new HashSet();
           return _StorageHistories;
     }
}

Of course if you go through the trouble of having a private anyway you might as well put it in the constructor.