Comments on: Must Everything Be Virtual With NHibernate?

By: Setting up NHibernate with SQLite using Visual Studio 2010 and NuGet | Coding Journal

Tue, 25 Oct 2011 22:54:27 +0000

[...] Note the virtual keyword everywhere. Must everything be virtual with NHibernate? [...]

By: Alejandro Payares

Alejandro Payares — Tue, 13 Sep 2011 14:35:00 +0000

Very clean and precise explanation. Thanks!

By: YiWei _ reproduced: I feel to NHibernate (2) : why should fully everywhere

YiWei _ reproduced: I feel to NHibernate (2) : why should fully everywhere — Thu, 08 Sep 2011 05:49:25 +0000

[...] you see the NHibernate development team membersDavy BrionArticle"Must Everything be Virtual with NHiberante？"Later, I know their design ideas-although I still don’t agree.I really don’t like [...]

By: Build Your Own Data Access Layer: Lazy Loading

Build Your Own Data Access Layer: Lazy Loading — Sun, 04 Sep 2011 11:04:14 +0000

[...] NHibernate has a similar restriction and i've tried to explain the reasons behind this in this post.I'm not sure if i succeeded in explaining this topic in a simple and clear manner, but this [...]

By: Why NHibernate Entities Need A Public Or Protected Parameterless Constructor

Why NHibernate Entities Need A Public Or Protected Parameterless Constructor — Sun, 04 Sep 2011 10:36:49 +0000

[...] then NHibernate will create a type which inherits from your entity (this is described in depth here and here). Which means that we really need either a public or protected constructor in entity [...]

By: Karl Cassar

Karl Cassar — Wed, 01 Jun 2011 22:36:00 +0000

A small note to anyone reading this in the future – One can easily bypass the virtual checking by adding the property ‘use_proxy_validator’ set to false in the nhibernate config.

config.SetProperty(NHibernate.Cfg.Environment.UseProxyValidator, “false”);

http://www.nhforge.org/doc/nh/en/index.html - Section 3.5.2

By: fluent nhibernate mappning | Maffelu.net

fluent nhibernate mappning | Maffelu.net — Sun, 22 May 2011 16:28:37 +0000

[...] Det enda man måste tänka på är att göra egenskaperna virtual så att nHibernate kan skapa sina proxy klasser. För att skapa mappningen så måste vi ha i åtanke att vi faktiskt jobbar med arv och att även [...]

By: Theo de Roo

Theo de Roo — Tue, 09 Nov 2010 04:36:17 +0000

This is all well and good and very useful, until the classes you want to map to NHibernate implement for example INotifyPropertyChanged (crucial for data-binding). Events have to be declared virtual as well for NH to be able to make proxies. However, when you happen to be developing in VB2005/2008/2010 then you know that the compiler does not allow you to define events (even custom events) as virtual/overridable! So why does NH need to have events virtual as well? Because the proxy instance is not the same .NET instance as the initialized proxy. Hence, any control which subscribes to the event of an object, could be subscribing to a proxy. However once the event fires it does so from another instance, hence you would never receive it. My solution is to create a C# base class which implements INotifyPropertyChanged and allows virtual events. And have all my VB classes inherit from it. Stupid, strange and frustrating, but hence is the standardisation across .NET compilers…

By: Starting NHibernate | Adding DLLs, Mapping Tables to Objects « CowFarm.NET

Thu, 05 Aug 2010 14:00:52 +0000

[...] The dumb answer to the first question is because Nhibernate will throw a “NHibernate.InvalidProxyTypeException“. This goes for anything that is exposed outside of your Object. The fastest answer I can give you is, in order to lazily load your objects. Many blogs already cover why, I recommend reading Davy Brion’s Blog post: Must everything be virtual with nhibernate?. [...]

By: Tony S

Tony S — Wed, 23 Jun 2010 12:47:19 +0000

In the NH mapping files on the class eleent there is an attribute named “proxy”.
This will allow you to use an interface to desctibe which properies/methods you want to lazy load.

I do agree any objects the UI consumes should be DTO’s, and this would also negate some of the issues.

By: Davy Brion

Davy Brion — Mon, 17 May 2010 15:21:07 +0000

@Mathieu

http://davybrion.com/blog/2010/05/why-you-shouldnt-expose-your-entities-through-your-services/

By: Mathieu Clerte

Mathieu Clerte — Sun, 16 May 2010 13:14:28 +0000

DTO? No… Why?

My issue was that in my DataAccess Layer I have Entities loaded using Criteria API, lazy=true, and those are returned in the Service Layer, which serialize (WCF) the entity , thus accessing the properties, which trigger the proxy crap.

I just want the serializer to access the property as it is , without re-querying the DB as we are now in the service layer and not in the DAL. I don’t want to make changes at the serializer level.

In my opinion, using DTO in this case is a too bulky solution…

- create a new DTO class for each specific need leads to a huge number of class at the end unmanageable

- filling DTO from Entities require either a deep copy / recursive reflection / (serialization/deserialization) operation which is very consuming

In my case I absolutely want to return the Entities but i need a way :

- either to remove the proxy crap from the entity (I found this Hibernate proxy cleaner that I need to convert for NHibernate in C#.

- either to disable the proxy so that IF the NHibernate session is closed, the proxy does NOT try to retreive any data (I think this is missing from nhib.)

If anyone has ideas….

By: Davy Brion

Davy Brion — Wed, 12 May 2010 06:57:33 +0000

@Ciaran

why even send the entities over a WCF service anyway? you’re much better off mapping to DTO’s and sending them over the wire. You’ll have complete control over what gets sent and what doesn’t.

By: Ciaran

Ciaran — Wed, 12 May 2010 05:56:37 +0000

I’ve been trying to disable lazy loading in nHibernate as I’m storing some blobs in my database. So I have a Document table and a DocumentContent table. Document contains a filename, description etc and has a DocumentContent property.

I have a Silverlight client, so I don’t want to load up and send the DocumentContent to the client unless I explicity ask for it, but I’m having trouble doing this. In WCF serialization the DocumentContent property will be touched and so gets lazily loaded then. I’m trying to turn this off and have added lazy=false and removed virtual from my classes but it’s still loading

I have a posting on StackOverflow about this and would be grateful if you could have a look: http://stackoverflow.com/questions/2816243/prevent-lazy-loading-in-nhibernate

By: 1000niaz نيازمنديها

1000niaz نيازمنديها — Sun, 02 May 2010 20:47:43 +0000

btw, you can just as easily get a proxy without going through an association by calling session.Load instead of session.Get.

By: Afshar Mohebbi

Afshar Mohebbi — Wed, 28 Apr 2010 11:11:47 +0000

Thanks Davy,
We turned our lazy-disable Nhibernate application into lazy with this good blog post.

By: Starting NHibernate | Mapping Tables to Objects « CowFarm.NET

Starting NHibernate | Mapping Tables to Objects « CowFarm.NET — Wed, 21 Apr 2010 20:06:26 +0000

By: My first NHibernate application « Dilhan's Blog

My first NHibernate application « Dilhan's Blog — Wed, 24 Mar 2010 08:55:34 +0000

[...] can create required proxy class for our class types. For more info about this please read this post by Davi Brion. Also the collection types shuold be IList<> or ISet. (e.g. [...]

By: Setting up Table/Object mappings using Fluent nHibernate – Matt Long (.com.au)

Mon, 08 Feb 2010 19:21:32 +0000

[...] proxies to achieve its Lazy Loading feature. This is a bit beyond the scope of this post, but Davy Brion offers a pretty detailed explination, The quick answer to that question is: because we need members to be virtual in order to do our [...]

By: Must Everything Be Virtual With NHibernate, Part II | The Inquisitive Coder – Davy Brion’s Blog

Wed, 23 Sep 2009 04:56:39 +0000

[...] already tried to explain this before, but here’s a simple example from a presentation i recently did on [...]