Comments on: Fetching Strategy NHibernate Implementation Available

By: Stepping onto the Bus | YOOT

Stepping onto the Bus | YOOT — Mon, 12 Oct 2009 21:01:15 +0000

[...] querying in a true DDD fashion is the notion of Fetching Strategy (read more about it here & there). We need Fetching Strategies for a very simple [...]

By: Living in the Tech Avalanche Generation » Entity Framework 4.0 and Fetching Strategies

Wed, 29 Jul 2009 10:13:17 +0000

[...] of sorts. Udi has written extensively on this and developed a method for using fetching strategies with NHibernate and if you haven’t yet checked out what he’s had to say to date on the subject I suggest you [...]

By: udidahan

udidahan — Wed, 04 Mar 2009 13:30:43 +0000

Chris – it’s a part of his rhino tools. Get it here:

https://rhino-tools.svn.sourceforge.net/svnroot/rhino-tools/trunk

By: Chris Cyvas

Chris Cyvas — Wed, 04 Mar 2009 11:08:13 +0000

Hi Udi,

You mention Ayende’s “repository bundles” – can you be more specific?

Thanks,
Chris

By: Living in the Tech Avalanche Generation » Entity Framework, Repositories, Specifications and Fetching Strategies Part 9.0

Mon, 23 Feb 2009 09:12:48 +0000

[...] causing persistence and my favoured approach to this is a highly configurable an tunable one. Udi demonstrates this using NHibernate and Fetching [...]

By: udidahan

udidahan — Thu, 02 Oct 2008 21:00:41 +0000

Wadaa,

Ayende’s new repository bundles this behavior into it directly. Use it

By: wadaa

wadaa — Thu, 02 Oct 2008 20:35:25 +0000

how will this work in the new nhibernate 2.0 binaries, the Create method you created doesn’t exist anymore. i’m especially wondering how this works with the nhibernate.linq extension from ayende, how can you put the criteria in those queries (_query = unitOfWork.Session.Linq()).

By: Living in the Tech Avalanche Generation » LINQ To SQL, Dynamic Querying & Fetching Strategies (cont)

Tue, 15 Jul 2008 05:49:02 +0000

[...] to come back with an approach on enabling Eager Loading by implementing a Fetching strategy (ala Udi), that can be used with my Repository. Here’s the Fetching Strategy code (most of [...]

By: QCon London 2008 Recap

QCon London 2008 Recap — Thu, 20 Mar 2008 09:07:31 +0000

[...] It leads to IFetchingStrategy for improved database loading performance (also a year old – better DDD implementation and the NHibernate implementation). [...]

By: Colin Jack

Colin Jack — Thu, 04 Oct 2007 11:31:04 +0000

Ok pasting in the example failed again Basically I think if you put in “hibernate.hbm2ddl.auto” as “create” it’ll generate the schema for you (page 23 of NHibernate reference doc).

By: Colin Jack

Colin Jack — Thu, 04 Oct 2007 11:29:45 +0000

Na thats a valid point, its definitely configurable. Like I say the strategy approach and we may well try it out.

The bit I tried to put in about the create schema stuff got cut out but its basically this (replaced

By: thesoftwaresimplist

thesoftwaresimplist — Fri, 28 Sep 2007 15:38:09 +0000

The solution you describe sounds like it would end up in the same amount of code as mine. The main difference is that the fetching strategy is injected in my case, so you wouldn’t have to change any code, just config files, to get it to work. This makes it quite easy to test the system with various combinations of fetching strategies and see which performs best.

I’ll do a double-check on the technology aspects (DB Schema and unit tests).

Thanks Colin.

By: Colin Jack

Colin Jack — Fri, 21 Sep 2007 15:17:25 +0000

The DB schema you’ve provided doesn’t seem to work but I added this line withing the section to get it to auto create the database structure:

create

Anyway, having domain classes having to implement multiple interfaces, one for each use case, seems like it might become a bit of a drag. I don’t mind interfaces but I hate anything that forces me to put interfaces onto the domain classes if I don’t really feel they really improve the design.

I also don’t really mind the service layer being dependent on the actual domain classes, I’m unlikely to need to swap out one Order implementation for another and if I do the interface I derive from this approach might not suit.

However like you say there are still the performance/responsibility issues.

With these two issues in mind I’m wondering if a solution isn’t just to have a domain service layer and you could have a service class specifically setup to handle each case. Our project has just such a layer, for other reasons, so I would say that I’d far rather that layer (which is on top of the domain but which clients can view as being part of the domain) took over the responsibility. For me that layer is the one that can talk to the repositories/fetching strategies to do the sort of coordination you describe.

I still like the fetching strategy approach though, but I’d just let this domain service layer take the responsibility for choosing which strategy object to use.

I was also thinking, your example relies on people having the VSTS unit testing stuff which might hamper a lot of people who want to try it out.