ORM (esp. NHibernate) performance for complex queries

Question

My company is in the process of rewriting an existing application from scratch. This application, among other tasks, performs complex SQL queries against order and invoice data

Answer 1

NHibernate has a bit of a learning curve, but it is well worth learning as any time spent will pay off many times over. I would recommend NHibernate in Action book for learning as it is an excellent resource and covers everything your question asks and a whole lot more.

NHibernate performance can be tuned (see links below) and NHibernate has robust caching mechanism.

http://www.codeproject.com/KB/database/NHibernate_Perf.aspx https://www.hibernate.org/hib_docs/nhibernate/html/performance.html

Ultimately the performance will be determined by who writes the queries as it is in SQL.