Friday, 10 October 2008

What I've got against NHibernate

Apart from being another example of too much configuration in XML? Well Billy McCafferty has summed it up for me in his article on CodeProject

Your database should be an "implementation detail" that is defined to support your domain model, not the other way around.
No it shouldn't. This is backwards for all but the largest businesses with lots of DBAs and data warehouses. This is a very arrogant developer argument to make.

It is more important to the business to be able to quickly and accuratly report about the business than to sell one more widget. Getting timely and accurate information about the widgets you've sold is more important. I know of lots of businesses who sold lots of their product and still went bust, owing to poor finanical management. Every business has to be able to manage their cash-flow at least as well as they can sell, and the database should represent this. Programmers can make the program more flexible to fit in with the best design for the business, but database design should be driven by business requirements, not programmers' whimsey.

In many, many cases both of these requirements will be in alignment, but not always. Some of your objects may need to populate and be populated from multiple tables, and whilst NHibernate can support this, it does drive developers to generate a 1-1 database model matching their entities.

And another thing, Billy doesn't hint at this, but says it explictly.

it is commonly accepted by many that ORM technologies, when used correctly, are, in fact, a silver bullet for software development
No they're not - don't be stupid. ORM technologies are a useful shortcut for developers to do less boring code, but they are not a silver bullet. They do not replace data abstraction layers, mearly form part of it. ORM is about being able to maintain the state of your objects in a database. Databases do more than just store developer's objects - how arrogant is this man?

Databases and DAL often perform complex data manipulation required by the business. Sometimes you need a process which will derive data from inputs, and you need a manageable, maintainable design pattern to implement these processes with data decorators and transformation objects. Whether you choose to put this code in NHibernate or elsewhere, then it still needs to be done. Using NHibernate doesn't remove business requirements.

1 comment:

Anonymous said...

I totally agree with you. NHibernate is only useful on green field projects where the domain model is well mapped to the database, otherwise it causes more problems than it solves.