For everyone who has read my article on NHibernate, here's a story for you...
When building an application, everyone comes to a point where one needs to batch-update records in a database table, based on one or more criteria. Let's say, for example, there's a table "User" containing an activation date. And you want to remove all users that have activated in 1999. In a regular database environment, or when using ADO coding, one would write a DbCommand "DELETE FROM User WHERE activationdate < '2000-01-01'".
This can also be done using NHibernate, by fetching an IList<User> from your database, and calling session.Delete(user); for each user in the list. Another idea is to use a HQL query: session.Delete("from User u where u.ActivationDate < '2000-01-01'"); A good thing about NHibernate is that it supports caching of data, but for this batch-delete purpose, it sucks. NHibernate will, in both previous cases, fetch all affected data, map it to objects, store it in first-level cache, ... Overhead galore!
Luckily, I saw a blog post on this by jlockwood. He simply tells to enlist a regular SQL statement in a NHibernate transaction, and you're ready to go. His code isn't provider-independent, so here's an improved version:
ISession session = sessionFactory.GetSession();
using(ITransaction transaction = session.BeginTransaction())
IDbCommand command = session.Connection.CreateCommand();
command.Connection = session.Connection;
command.CommandText = "delete from User where activationdate < '2000-01-01'";
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