Ayende @ Rahien

Ayende Rahien commented on NHibernate Mapping – Inheritance

Fri, 05 Jun 2009 13:30:27 GMT

Dave, Please post the full details to nhusers

dave commented on NHibernate Mapping – Inheritance

Fri, 05 Jun 2009 03:38:42 GMT

Sorry the code should have been like this. (it seems the commect are accepting my less then tags and parsing them as HTML do I smell XSS attacks)

dave commented on NHibernate Mapping – Inheritance

Fri, 05 Jun 2009 03:34:59 GMT

Hi, I am doing "table per subclass" with this exact same DB schema, However I also have a related table called Address which links to Party The XML mapping file will not allow me to use both joined-subclass for my Company and Invervidual. When I try to include my address into Party via join. Is there any way around this? (p.s I am only new to nHiberbate) for example --------------------------

Ayende Rahien commented on NHibernate Mapping – Inheritance

Tue, 05 May 2009 05:47:57 GMT

Chris, On the face of it, I don't see why no.

Chris Nicola commented on NHibernate Mapping – Inheritance

Tue, 05 May 2009 00:07:32 GMT

Can the Unioned-Subclass (or any other approach) be applied to interface classes instead of abstract classes? If I have two tables which map to classes that implement the same interface can I setup something where I can get all the objects from both classes with one query on the interface class?

Krzysztof Kozmic commented on NHibernate Mapping – Inheritance

Sat, 11 Apr 2009 13:37:35 GMT

I see, I've read in few places discussion on pros and cons of each approach. However, I think you, as someone who knows NHibernate in and out, could give a much better and in-depth explanation of the topic. Maybe some other time then.

Ayende Rahien commented on NHibernate Mapping – Inheritance

Sat, 11 Apr 2009 09:39:19 GMT

sebastijan, HiLo can generate a unique ID without having to go to the database. It has all the benefits of GUIDs, but without having to deal with the GUID opaque nature.

sebastijanp commented on NHibernate Mapping – Inheritance

Sat, 11 Apr 2009 09:33:59 GMT

Why is hilo generator "generally much more recommended anyway"? Does it has to do with optimization? What are the benefits over the identity?

Ayende Rahien commented on NHibernate Mapping – Inheritance

Sat, 11 Apr 2009 08:13:43 GMT

Trent, There are different optimizations and constraints that apply to each of those. See David's comments for some of them.

Ayende Rahien commented on NHibernate Mapping – Inheritance

Sat, 11 Apr 2009 08:12:10 GMT

alberto & Krzysztof, It is a matter of time and place, actually. Those posts are part of the prep work for the NH course that I am about to give in May. They represent about 3 hours of discussion of scenarios, alternatives and motives. Pretty hard to put into words by typing them. And most of the info is already out there.

huey commented on NHibernate Mapping – Inheritance

Sat, 11 Apr 2009 05:11:02 GMT

@justin Thanks, I'm stupid and glossed over the fact that session.get(userID) was grabbing all of the potential data for employee and vendor so I could later cast appropriately.

Trent Foley commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 18:00:03 GMT

It seems to me that 95% of the time you would want to use the first method mentioned (Table per Hierarchy). This has been the approach I have taken to date, and has been painless so far. The other 5% of the time I imagine would be due to having to map to an existing database, or you are working with a DBA who is a Normilazation Nazi.

David commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 17:24:57 GMT

@alberto and @Krzysztof from my limited understanding. table per concrete class - fastest, harder to do polymorphing, bad thing you have to update all the tables if there is a change at the parent class level. table per hierarchy - fast, but your columns cannot must allow nulls (as multiple classes will not use them), easy for reports. table per subclass - this is meant to be the slowest (for large projects), I have no proof, but it the best way for normalisation, clean data. So the design looks nicer. the books i would reconmend NHibernate in Action, this has a section on this. Patterns of Enterprise Application Architecture Also thank you Ayende for doing these posts.. I am finding them great for reference!

Dmitry commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 17:17:14 GMT

I did not know about the union class either. I do not think it has mentioned that you can use common base classes or interfaces to do polymorphic queries. So commands like session.CreateCriteria(typeof(object)).List() or session.CreateCriteria(typeof(IEntity)).List() (assuming it's a common interface for the entities) are legal in NHibernate.

justin commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 16:44:16 GMT

@huey Polymorphism is your friend. User user = session.Get(userId); Vendor vendor = user as Vendor; Employee employee = user as Employee; Lookup the "as" and "is" keywords and also remember you can do explicit casting Vendor vendor = (Vendor)user;

huey commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 15:31:43 GMT

Dumb question. I might have to make a website for our vendors. So it is going to have type user and a user might be an employee or vendor. Both employee / vendor will share the same user table and have unique user id's. This seems to fit in with inheritance mapping in NH. The thing is, in all cases I'm going to start with a user id and the first thing I'm going to want to do is figure out if the user is an employee or a vendor. So it might be something like: User user = session.get

Tomasz Modelski commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 11:57:42 GMT

@ meo : check the date of this news .... :-)

alberto commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 11:54:51 GMT

I'm with Krzysztof. It's something I've missed in the series. It feels like some scenarios would help to understand when to use each approach.

meo commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 09:31:18 GMT

Did ya read this? [blog.wekeroad.com/.../subsonic-to-acquire-nhibe...](http://blog.wekeroad.com/subsonic/subsonic-to-acquire-nhibernate/)

Krzysztof Kozmic commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 07:18:09 GMT

I didn't know about union-subclass. Interesting. There's one thing I think would make a great addition to these posts - insight. Showing the mappings and SQL in a very manual-like way is sure great but I wish you took it one step further and talked about non-obvious strengths and weaknesses of each approach. Good to see you blogging regularly again :)

pcm commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 06:23:32 GMT

As communicated in the email. I am open to delete this comment if it had hurt you. I love what you are doing for the community. I am also changing my name to acronym. And Also not using a link if that makes you happy.

Ayende Rahien commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 06:00:50 GMT

Hire, a) please use a real name, not a ad. b) I don't know if you noticed, but I didn't mention NH Prof in these, and they are talking about basic feature of NH.

HireDotnetexpert commented on NHibernate Mapping – Inheritance

Fri, 10 Apr 2009 05:49:51 GMT

Although these posts are geared towards your COMMERCIAL product, they are very helpful.