Comments on: Fetching Strategy NHibernate Implementation Available

By: udidahan

udidahan — Sat, 19 Jun 2010 20:56:20 +0000

Tom,

What I mean is also bypassing the object model that is mapped by your ORM in the case of queries, or setting up a custom object model that is used only for queries.

By: Tom

Tom — Fri, 18 Jun 2010 17:57:52 +0000

Thanks for replying but sorry not quite sure what you mean on your last comment about the “Even if you’re not using CQRS entirely, you can get a lot of benefits by circumventing your ORM for queries and working closer to SQL there.”

Also in regards to “IShowLatestResults” (home page) and “IShowFixtures” are those roles you would make explicit? Do they sound sensible or would it become unmanageable as they get added for each page almost..

By: udidahan

udidahan — Fri, 18 Jun 2010 14:34:50 +0000

Tom,

If you can use a container then you can resolve the IFetchingStrategy with it. Your main issue would be trying implement other ORM features. Even if you’re not using CQRS entirely, you can get a lot of benefits by circumventing your ORM for queries and working closer to SQL there.

Hope that helps.

By: Tom

Tom — Fri, 18 Jun 2010 14:10:52 +0000

Sorry I just read that back just to clarify:

Home page… only shows fixtures
Dedicated page ..shows fixtures and gamesheets

By: Tom

Tom — Fri, 18 Jun 2010 14:08:43 +0000

Also if not using CQRS, which is a bit overkill in my situation, what would you suggest for basic listing on a web page. My website is a hockey website and for example the home page shows Fixtures (matches) these have gamesheets about the fixture played, however I only want to show this on its dedicated page. I assume you would need to add something like “IShowLatestResults” (home page) and “IShowFixtures” on the aggregate Fixture.

I am keen to do this right, ive got to the stage of just wanting a simple solution that works is maintainable and most of all makes sense. Which I believe your solution does. Your InfoQ video about this subject when you said “for god sake let me build a system” is so true. Will be attending Skills Matter in London for the FAQ session. Do you have any content you will focus on? Or will it be all FAQ?

By: Tom

Tom — Fri, 18 Jun 2010 08:08:33 +0000

Yes those are fine, something like Windsor or Unity would be fine. Its basically plain ADO.NET. So I assume I would need to build up the query dynamically (and have to convince the DBA that dynamic sql isnt always bad!)

By: udidahan

udidahan — Fri, 18 Jun 2010 07:35:07 +0000

Tom,

Are you allowed to use existing dependency injection technologies or do you have to implement those yourself as well?

By: Tom

Tom — Thu, 17 Jun 2010 22:30:58 +0000

Hi,

Very interested in your example. I have tried your sample code but unable to get it run (database and runtime issues). How would you pre pose to add this to a in-house ORM? As we are not allowed to use things like Hibernate. I would love to this example up and running I understand the concepts but waiting for it all to “click” so I can implement myself.

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.