What\'s the difference between Get
and Load
? The documentation pretty much reads the same. Also, if it matter
http://ayende.com/Blog/archive/2009/04/30/nhibernate-ndash-the-difference-between-get-load-and-querying-by.aspx
Get will return null if the object requested doesn't exist. Load will throw an exception if the object requested doesn't exist. Otherwise, they function exactly the same as far as I can tell.
Load is the optimized way in some cases. Let's think of a Customer, Order relationship and assume that we have an Orders table with CustomerId as the foreign key.
var order = new Order {OrderDate = Datetime.Now };
order.Customer = session.Get<Customer>(customerId);
session.Save(order);
Although we only need the customerId to persist the order object, above code block will first select the customer with that customerId from Customers table then hit the database again to insert the order for that customer.
But if we used :
order.Customer = session.Load<Customer>(customerId);
only the insert statement with that customerId will be executed. Load is the appropriate way in this case.
The reference provided by Brian explains it quite clearly. However, the main difference is that Load
doesn't hit the database to check and load the entity you require, since it assumes you know the entity exists. The object returned by Load
is some kind of proxy that lazily fetches the real data when required or throws an exception if the entity is not found.
Recap:
Load
should be used when you know for sure that an entity with a certain ID exists. The call does not result in a database hit (and thus can be optimized away by NHibernate in certain cases). Beware of the exception that may be raised when the object is accessed if the entity instance doesn't exist in the DB.
Get
hits the database or session cache to retrieve the entity data. If the entity exists it is returned, otherwise null
will be returned. This is the safest way to determine whether an entity with a certain ID exists or not. If you're not sure what to use, use Get
.
Get will return Null if the object doesn't exist whereas Load will not return Null - it either returns an object or throws an exception.