Ayende @ Rahien

Kasi Prasad commented on Common infrastructure? Don't make me laugh

Sun, 23 Nov 2008 08:14:59 GMT

I have to agree with Oren and Colin. Repositories need to be molded against the application their being used for. What if I don't want my repositories responsible for persisting information and want to use a separate unit of work implementation (which i do) and I instead want my repositories to be query-able. In fact that's all I really want them to do; provide the ability to find things in my domain.

Colin Jack commented on Common infrastructure? Don't make me laugh

Sun, 16 Nov 2008 14:55:43 GMT

I think the comments might be going off course, IRepository

Ritesh Rao commented on Common infrastructure? Don't make me laugh

Fri, 14 Nov 2008 15:38:24 GMT

Hi Oren, I had posted some blog posts on my thoughts on implementing a Repository pattern based on the IQueryable. The beauty of using IQuerable as the uderlying base for the repository is that it further decouples the repository from infrastructure concerns, that is assuming that the underlying infrastructure provides an IQueryable implementation (something that NHibernate needs badly). Couple that with composable specifications that uses lambda expressions, that provides a lot of power. [www.codeinsanity.com/.../...ng-repository-and.html](http://www.codeinsanity.com/2008/08/implementing-repository-and.html) [www.codeinsanity.com/.../...ance-and-ddd-with.html](http://www.codeinsanity.com/2008/08/persistence-ignorance-and-ddd-with.html) BTW, love your blog. Thanks! - Ritesh

Bryan Watts commented on Common infrastructure? Don't make me laugh

Fri, 14 Nov 2008 06:23:34 GMT

And of course those should all be generic types, especially QueryableRepository{T, TSource} : Repository{T}, IQueryableRepository{T} where TSource : IQueryable{T}

Bryan Watts commented on Common infrastructure? Don't make me laugh

Fri, 14 Nov 2008 06:20:05 GMT

> I usually think about IQueryable as mutable. Linq is a functional approach to querying. Immutability is a core concept - queries are deferred and can be defined and composed without side effects. IQueryable defines the potential to be queried - the queryee (?) determines what a query actually means. Here is my take on IRepository (in use in personal libraries): === Interfaces === public interface IRepository : Repository > where TEntity : class { #region Static private static Table

Rob commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 21:32:10 GMT

What do you consider a good repository interface?

Colin Jack commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 21:09:28 GMT

@Rob I guess that example just emphasizes what Ayende is saying because I don't consider that a good repository interface, emphasizing that you need to evolve your own designs in these sorts of cases.

Ayende Rahien commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 14:40:34 GMT

Hm, I usually think about IQueryable as mutable. I guess it doesn't have to be.

Rob commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 14:29:10 GMT

I'm not sure I see what you mean. Since repository is queryable you can build any number of queries against it. var r = from c in CustomerRepository where c.Balance > 0 select c; or better yet, build specifications that are extension methods on queryable and in your service layer do stuff like: return customers.ThatAreActive().WithOutstandingBalance()

Ayende Rahien commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 14:20:48 GMT

Rob, The problem with that is that assume that you have a single query per repository.

Rob commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 14:14:59 GMT

My generic parameters got eaten in the comment above if that wasn't obvious. IRepository of T : IQueryable of T

Rob commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 14:13:24 GMT

If you base your repository around IQueryable then it becomes much simpler and easier to reuse. That will be more of a possibility for you I guess when LINQ to nHibernate is a little further along. Something like: public interface IRepository

Dave Newman commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 14:01:01 GMT

Maybe the DDD style Repository is worth another look?

Colin Jack commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 08:54:51 GMT

Couldn't agree more with this point and I like the technology infrastructure and application infrastructure split.

J Healy commented on Common infrastructure? Don't make me laugh

Thu, 13 Nov 2008 06:09:47 GMT

I agree somewhat with your assertion around technological vs. application infrastructure, but that whole discussion quickly starts turning around the semantics of "application" and what 'services/functionality' such an infrastructure might expose / provide. When you say: "multiple projects that aren't closely matched" - I think you are getting closer to the mark relative to such "common infrastructures" overreaching. In some sense I feel you do simply run up against a sweeping 'lowest common denominator' factor that casts a clear light on the risks of overreaching beyond a certain point. Azure and all the other PaaS offerings are probably a pretty good indicator of that "lowest common denominator" factor at work relative to where the 'natural' boundaries lie between "technological" and "application" infrastructures. But even there I suspect any significant apps you might build atop Azure, Gears, or EC2 would in fact exhibit enough common [admin] code to constitute something one might call a "common application infrastructure". You can argue how thick or thin that stack might be, but I suspect, once recognized, most pragmatists would resue that body of code, however derisible or unclean the exercise might feel due to other sensibilities.