Is it possible to use NHibernate without altering a DDD model that is part of a framework

Question

I dig a lot of things about the DDD approach (Ubiquitous language, Aggregates, Repositories, etc.) and I think that, contrary to what I read a lot, entities sho

Answer 1

In my experience, the only thing that NHibernate requires of a domain is virtual properties and methods and a default no-argument constructor, which as Jeff mentioned, can be marked private or protected if need be. That's it. NHibernate is my OR/M of choice, and I find the entire NHibernate stack (NHibernate, NHibernate Validator, Fluent NHibernate, LINQ to NHibernate) to be the most compelling framework for persisting POCO domains.

A few things you can do with NHibernate:

• Decorate your domain model with NHV attributes. These constaints allow you to do three things: validate your objects, ensure that invalid entities are not persisted via NHibernate, and help autogenerate your schema when using using NHibernate's SchemaExport or SchemaUpdate tools.
• Map your domain model to your persistent storage using Fluent NHibernate. The main advantage, for me, in using FNH is the ability to auto map your entities based on conventions that you set. Additonally, you can override these automappings where necessary, manually write class maps to take full control of the mappings, and use the xml hbm files if you need to.
• Once you buy into using NH, you can easily use the SchemaExport or SchemaUpdate tools to create and execute DDL against your database, allowing you to automatically migrate domain changes to your database when initilizing the NH session factory. This allows you to forget about the database, for all intents and purposes, and concentrate instead on your domain. Note, this may not be useful or ideal in many circumstances, but for quick, local development of domain-centric apps, I find it convenient.
• Additionally, I like using generic repositories to handle CRUD scenarios. For example, I usually have an IRepository that defines methods for getting all entites as an IQueryable, a single entity by id, for saving an entity, and for deleting an entity. For anything else, NH offers a rich set of querying mechanisms -- you can use LINQ to NHibernate, HQL, Criteria queries, and straight SQL if need be.

Th only compromise you have to make is using NHV attributes in your domain. This is not a deal breaker for me, since NHV is a stand-alone framework which adds additional capabilities if you choose to use NHibernate.

I have built a few apps using NH, and each has a persistence ignorant domain with all persistence concerns separated into its own assembly. That means one assembly for your domain, and another for your fluent mappings, session management, and validation integration. It's very nice and clean and does the job well.

By the way: your English is pretty darn good, I wish my French was up to par ;-).