Tuesday, August 07, 2007

Linq And Specifications

We've been puzzling about how to improve our use of the specification pattern.

In particular currently if we have a specification CustomerNameSpecification that acts over objects in memory then we want it to be joined up to the assoicated GetCustomersWithName method on the CustomerRepository.

Up till now this has been difficult, we don't want NHibernate to leak into the domain and so we've just kept the specifications as operating over in-memory objects and the associated queries on the repositories use ICriteria/HQL.

Then Linq came along. Now I'm no expert on it, tried it out an age ago and since I've only been reading about it but it does look interesting and there have been a few interesting articles about it, both from a single blog:

  1. Persistence Ignorance And Linq - Good introduction to how Linq can support DDD in .NET.
  2. Linq and Specifications - The section "Specifications and Repositories" is interesting. There is obviously a tradeoff as the specification gets more complex/abstract but the advantages could make it worthile.

Anyway its interesting stuff.

The specification approach is great and the idea of having in-memory repositories using Linq is detailed too. Neither are new ideas but both could be very important in the future and solve problems and its good to have articles on them. Also with Linq coming to NHibernate it'll be interesting to see what is possible.

Part way down one of the articles is a link to an example app, will have to look at it at some stage.

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