This
is part of a series of posts about NHibernate Pitfalls. See the entire collection here. When saving a new entity that has references to other entities (one to one, many to one), one has two options for setting their values: Load each of these references by calling ISession.Get and passing the foreign key; Load a proxy instead, by calling ISession.Load with the foreign key. So, what
is the difference? Well, ISession.Get goes to the database and tries to retrieve the record with the given key, returning null if no record
is found. ISession.Load, on the other hand, just returns a proxy to that record, without going to the database. This turns out to be a
better option, because we really don’t need to retrieve the record – and all of its non-lazy properties and collections -, we just need its key. An example: 1: //going to the database
2: OrderDetail od = new OrderDetail();
3: od.Product = session.Get<Product>(1); //a product
is retrieved from the database
4: od.Order = session.Get<Order>(2); //an order
is retrieved from the database
5:
6: session.Save(od);
7:
8: //creating in-memory proxies
9: OrderDetail od = new OrderDetail();
10: od.Product = session.Load<Product>(1); //a proxy to a product
is created
11: od.Order = session.Load<Order>(2); //a proxy to an order
is created
12:
13: session.Save(od);
So, if you just need to set a foreign key, use ISession.Load instead of ISession.Get.
