Linq Expression Evaluation

If you have a Linq Expresssion (such as a reference to a variable in the closure) or really any other self-contained fragment, you can easily evaluate it by turning it into a lambda expression. For example, I was trying to evaluate the content of a variable that was showing up as a ".x" field. To do so, I did the following:



 

NHibernate 3.0

NHibernate 3.0.GA has been released!  It has all sorts of goodies like QueryOver, logging abstraction, and tons more.  It also now has a built-in LINQ provider.  Unfortunately, the LINQ provider is still in a beta state.  Many queries work (as evidenced by the hundreds of working unit tests), but there are also still many queries it has trouble with.  If you'd like to help accelerate the development of the LINQ provider (or any other part of NH for that matter), here's what you can do:

1. File issues when you find bugs.  http://jira.nhforge.org/
2. Vote for issues.  Popularity is difficult to gauge if we don't hear back from people.
3. Provide test cases for those issues.  A complete test case is easier to digest than a tiny code fragment without context.  If the test can be used directly, the team member working on the issue can spend more of their time making improvements instead of trying to recreate a test.
4. If you're feeling ambitious, dig into the source code and try to work out a fix.

There's a great article on making tests for NHibernate here.  I've also included some different steps that might help you out.

1. Check out the trunk using something like TortoiseSVN (https://nhibernate.svn.sourceforge.net/svnroot/nhibernate/trunk/nhibernate)
2. Use ShowBuildMenu.bat to create the AssemblyInfo.cs files.
3. Load up NHibernate.Everything.sln in Visual Studio.
4. Create a test with the issue number in the NHSpecificTest folder of the NHibernate.Test project (NH2392 is a fairly simple example to copy from).
5. Use ShowBuildMenu.bat to see how to set up your database connection and run all the tests.
6. Create a patch (TortoiseSVN can help you with this) and attach it to the JIRA issue.

With your help, we will work towards a rock solid LINQ release that matches the tremendous power and reliability already provided by the NHibernate platform.

Interesting Changes in NHibernate 3.0

There are tons of new features in NHibernate 3.0. I'm going to highlight a few minor interesting ones from my view.

Client Profile Support
The .NET client profile is now supported out of the box.  Castle.Core also supports the client profile as well, so the Castle bytecode provider will work out of the box as well.  Great news for those who write desktop apps.

Logging Abstraction
In getting support for the client profile, log4net was an issue.  It hasn't been updated in ages and doesn't support the client profile itself.  This issue combined with other people's desire for a logging abstraction now means that NHibernate supports pluggable loggers.  You can use the NHibernate.Logging package to get support for libraries such as Common.Logging.  This also enables use of the excellent NLog framework, which is actively updated.

Polymorphism in Get and Load
Previously, Get and Load methods on the session required the exact mapped type.  Now, they allow you to specify a class or interface higher up the inheritance hierarchy, as long as there's only one match.  This will allow people to eliminate their own mapping layers when it comes to retrieving objects by primary key.  Importantly, this will make ActiveRecord work much better with interfaces.

Fixes for IdBag
The identifier bag had a bunch of bugs, especially ones that manifest themselves more when used in rich client applications.  If you had problems before, try it again.

ISQLFunction Argument Repetition
[Update: This will not be included in 3.0]

Though it's not in the trunk, I'm also excited about the potential inclusion of NH-2318.  This will let us write functions for dialects that have non-trivial argument patterns.  For example, a NullSafeEquals function could be written as (?1 IS NULL AND ?2 IS NULL) OR (?1 IS NOT NULL AND ?2 IS NOT NULL AND ?1 = ?2).  With the current code, such a function breaks because it repeats arguments.  The patch also deals with argument reording or removal, but it doesn't support ordinal parameters at the moment.  We'll see if this one happens to make it in.

All in all, NHibernate 3.0 is a very exciting release that many contributors have put a lot of hard work into.

Obtics

If you're working with .NET and any sort of observability, such as WPF bindings, you owe it to yourself to check out Obtics. It's an excellent library that turns an expression into an observable expression. It has full support for System.Linq.Enumerable methods and for arbitary expressions.

Using Obtics and a custom helper method, you can do things like:

public int AplusB
{
    get
    {
        return Getter(() => AplusB, () =>
            A + B
        );
     }
}

Now, whenever A or B change, a property changed notification is fired for AplusB.

Imagine now that the expression inside is not as simple as A + B but several lines of code involving collections, linq extension methods, and more. Obtics is able to automatically add observability to the entire complex expression.

Need to watch for changes to proerties in collections? Obtics has elegant ways of doing that too. It's a great library, very much worth checking out. In comparison to CLINQ or Bindable LINQ, Obtics has a focus on full expression support. Having full expression support is extremely powerful and Obtics seems to be an excellent implementation of it.

Pleasant Solutions

Starting a software company has definitely been one of the most challenging and enlightening experiences in my life. Owning a business takes a great deal of commitment and will to persevere. I am a partner at Pleasant Solutions, a custom software development house. We have a fantastic team and it's a joy to come to work every day and collaborate with these excellent individuals.

Specializing in custom software development is a difficult road on which to tread.  Although we are able to produce high quality tailored solutions for our clients, doing so profitably is a major challenge.  Thankfully, having excellent people allows us to adapt quickly to a broad range of tasks.  Developing certain infrastructure components has been very beneficial to us.  For example, we have a hiring system that allows us to screen our applicants in a more accurate and efficient way than reading resumes.  As another example, we significantly enhanced the open source ActiveWriter (with minor contributions to Castle.ActiveRecord and NHibernate along the way) to meet our needs.  In fact, we have continued to make improvements to our in-house tool to the degree that our developers need little knowledge of the nitty gritty of NHibernate in order to complete even complex business and data modelling tasks.  Building knowledge and experience into a tool has been very beneficial for us.  When we do our next project, we can bring along our past experience automatically, increasing quality and reducing costs.

We're still learning and exploring all the time, and we hope to continue to share our talent and passion for software development for years to come.

WPF and NHibernate Lazy Proxies

Using NHibernate proxies with WPF binding will likely leave you scratching your head at moments. There are at least two issues that can get in your way. The first of these is that objects with INotifyPropertyChanged implementations will not update when the property is changed. Even though the event is fired, the WPF value never updates itself. This is because WPF compares the source of the event against the object that it originally registered the event with. Since the source of the event is the actual implementation object hidden by the proxy, but the object WPF knows about is the proxy object, WPF ignores the event. The best way to fix this is to have the proxy object rewrite the property changed events. There is a detailed explanation and a simple implementation here, but be aware that it doesn't redirect events from the source but throws its own events when properties are set. The other issue you will sometimes run into is a strange null reference exception when setting the value of a dependency property. There is a bug in WPF where it doesn't properly handle the names of classes without any namespaces. Since the lazy proxy objects have no namespace, this bug pops up. The issue is fixed in WPFv4, but if you aren't able to upgrade, you can fix this by changing a line in Castle.DynamicProxy. In ClassProxyGenerator.GenerateCode, add the "Proxies." part to the following line: String newName = "Proxies." + targetType.Name + "Proxy" + Guid.NewGuid().ToString("N"); This should help anyone experiencing the error relating to DetermineWhetherDBNullIsValid.