NHibernate and the Unit of Work

BrianOConnell · November 17th, 2010, 01:18 PM

First of all fantastic book but I'm a bit confused about the use of the Unit of Work pattern and the implementation for nHibernate.

Page 254 shows the implementation of the NHUnitOfWork which seems fine. On the next page there is an NHibernate base repository created which is passed an IUnitOfWork. This is then used in the Add, Remove and Save methods. Committ does not seem to be called despite the description of the NHUnitOfWork saying nothing will be saved/removed until Committ is called.

Later on page 463 when doing the same thing the injection of the Unit of Work in the constructor remains but is not used at any point in the Repository. Errors? Or am I just missing something?

elbandit · November 17th, 2010, 03:58 PM

Hi Brian,

First off thanks for buying the book and taking time to post this question.

The reason I inject the unit of work in via the repository is because an atomic action may span more than one repository. If you take a look on page 245 you can see that there is a call to the unit of works commit method within the AddMember method. The business transaction commits when the service says so.. consider the following senario...

Code:

 
var customer = customerRepository.FindBy(cusomerId);
 
var order = new Order();
 
// populate the order...
 
order.Customer = customer;
 
customer.YearlyOrderSpendAdd(order.Total);
 
// The customer has now been modified and the order needs to be added..
customerRepository.Save(customer);
orderRepository.Add(order);
 
// we only want to call commit now because we don't want an error to occur
// and the customer be saved but not the order added.
// The commit ensures that what has been addded/changed/removed it committed
// in a transaction as an atomic event i.e. all or nothing
uow.Commit();

I hope that make sense? If not please let me know and I can expand.

Cheers
Scott

p.s. would be great if you could adda review to Amazon and give me some feedback when you have finished the book :0) cheers!

BrianOConnell · November 17th, 2010, 04:32 PM

Thanks for the quick reply Scott. Makes sense all right but you might take a look at the Repository implentation later on for the store (463-4 I think) where the unit of work is injected but not used as fas as I can see. I'll get a review up on amazon soon. Just on the last chapter :) My only complaint is the lack of unobtrusive javascript. A book with such an excellent run down of all the ellegant patterns out there should include the most elegant approach to javascript too imo.

elbandit · November 17th, 2010, 05:04 PM

Ah yes, blimey good spot. On page 463-4 i took a short cut and bypassed the unitofwork for the adding/removing/updating this was because I could use the same code straight from within the base repository class - basically I was lazy! Take a look in the NhUnitofWork class and you will see the same code. However all works in the same way and the unitofwork instance is still called to commit the business transaction. But your right it does make it confusing when there is no need to be!

Yes hands up on the JavaScript, I don't do a lot of JavaScript work so thats the reason why it's not as polished as the rest of the code examples.

Glad you enjoyed the rest of the book. I am in the process of adding support for entity framework and db4o in the case study as well as replacing the query object pattern with linq expression trees as most of the orms have a linq provider now.

Cheers
Scott

devnetfx · November 20th, 2010, 10:23 PM

Hi Scott,

I am looking forward to the replacement of Query Object pattern with linq expression trees. I hope the code will be available at aspnetdesignpatterns.codeplex.com

elbandit · November 21st, 2010, 09:04 AM

Hi devnetfx,

Yes should be up by the end of next week.

Scott