RavenDB & NServiceBus -

The upcoming version 3.0 of everyone’s favourite service bus, NServiceBus, will now use RavenDB for saga persistence.  This makes it even easier to work with sagas in NSB.

Very cool!  Even better than that, it looks like RavenDB will be available for NServiceBus Express users too.  You can read Udi’s comment here.

Big thanks to Ayende and Udi for getting these two elegant technologies together like this. 

Mocking DbContext Entity Framework 4 Code First CTP5 with NSubstitute

Take an Entity Framework 4 Code First model, something like this:

   1: public class Customer

   2: {

   3:    public int Id { get; set; }

   4:    public string Name { get; set; }

   5: }

   6:  

   7: public class CustomerContext : DbContext, ICustomerContext

   8: {

   9:    public DbSet<Customer> Customers { get; set; }

  11: }

I now want to write some tests and I'm going to mock the DbContext using NSubstitute.  I first try something like this:

   1: [Test]

   2: public void can_mock_customer_context()

   3: {

   4:    var context = Substitute.For<CustomerContext>();

   5:    context.Customers.Returns(

   6:       new DbSet<Customer>(

   7:          new[]

   8:          {

   9:             new Customer {Name = "Sean"}

  10:          })

  11:       );

  12:    Assert.AreEqual(1, context.Customers.Count());

  13: }

The problem is that the DbSet constructor is internal (as of EF4 Code First CTP5).  So, let's abstract our DB access to a simple interface and replace DbSet<T> with the IQueryable<T> interface, ending up with the below:

   1: public interface ICustomerContext

   2: {

   3:    IQueryable<Customer> Customers { get; set; }

   4: }

This interface can be implemented like so:

   1: public class CustomerContext : DbContext, ICustomerContext

   2:   {

   3:      public DbSet<Customer> Customers { get; set; }

   4:      IQueryable<Customer> ICustomerContext.Customers { get { return Customers; } }

   5:   }

Now all we need to do is to use an implementation of IQueryable<T> in our mock.  I'm going to use EnumerableQuery<T> which gives me the following test that now passes:

   1: [Test]

   2: public void can_mock_customer_context()

   3: {

   4:    var context = Substitute.For<ICustomerContext>();

   5:    context.Customers.Returns(

   6:       new EnumerableQuery<Customer>(

   7:          new[]

   8:          {

   9:             new Customer {Name = "Sean"}

  10:          })

  11:       );

  12:    Assert.AreEqual(1, context.Customers.Count());

  13: }

  14:    }

I'm new to NSubstitute but it seem to be the lowest friction mocking library out there.  Just perfect for use with Entity Framework 4 Code First - certainly the lowest friction ORM there is today!

Note that we could have used the repository pattern to wrap the DbContext instead of a simple interface, the approach is almost identical.

Update: Ro Miller has an alternative approach using fakes that does a better job of surfacing IDbSet.  Check it out here: http://romiller.com/2010/09/07/ef-ctp4-tips-tricks-testing-with-fake-dbcontext/.

Package Manager With Source Download

I was skinning up some code and I used my package manager of choice to add NLog to the project.  All good, very easy and away I coded.

The project required a single DLL as an output.  So, I thought hey – I’ll use Paul Stovell’s Tape to save using ILMerge in the build.  Good plan, but after 5 minutes browsing the NLog source on GitHub it realised I was not sure how to find the version I needed.  That’s fine, ILMerge is pretty easy to use so I used the build to save the day.

On the same day (today) I read this post about ReSharper 6 features and suddenly realised how powerful it would be for package managers to be able to give me the source, not just binaries.  Now that’s a killer feature and would be even better if the source came with a single file option so I didn’t even have to run Tape.

Oh, please, soon…

A Better Deal

Red Gate are now going to charge for Lutz Roeder’s Reflector.  This tool has been free for it's life – more years than I care to remember.  Its as much part of a software developer’s toolkit as a hammer is part of a builder’s toolkit.

I have dealt with Red Gate as part of a very small company and as part of a very large company.  I am sorry to say that each time I have come away feeling less than happy.  Any company that sends be a maintenance bill at the end of year one that exceeds my original purchase price isn't going to make me happy to deal with them!

Reading Red Gates’ pricing strategy, written by their co-founder, Neil Davidson, I struggle to believe their other CEO, Simon Galbraith, when he says how sorry he is about charging for Reflector.  I just kept thinking that they just want my cash - like the other times I’ve dealt with them.

Maybe Galbraith and Davidson should go and listen to Seth Godin’s pricing advice.  Maybe then I’d want to buy stuff from them! 

35USD is good value for Reflector and I may have to buy a copy.  I’d really just rather buy from another company and get a better deal.

Install the Full .Net 4 Framework with Tarma Installer

If you haven’t seen Tarma InstallMate before, the you need to check this little beauty out.  It’s a fully featured installer that  have been using it in production for just under a year now and the end-user setup installer just drops out of the end of my build process – sweet!

There’s one thing that is very different with Tarma and all the other installers out there – Tarma doesn’t charge stupid rip-off money like all the other suppliers seem to like to do.  You can get their top-of-the-range product for under $90USD per developer.  Couple that with totally superb support, rock solid performance and a really rich feature set, Tarma’s a total winner!

Out of the box, Tarma has support for a number of prerequisites like .Net Framework, Access runtimes and Windows Installer.  However, it doesn’t differentiate between the Full and Client Profiles for .Net 4 – if the Client Profile is detected then it will not install the full framework and I need to get the full framework onto my user’s machine. 

Detecting the Installed Framework Version

To detect which version of the .Net Framework 4 has been installed, you need to check the presence of the following registry keys.

HKLM\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Client
HKLM\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full

More details on that here.

We can set up Tarma to do that easily, like this:

Read Registry Key into a Variable

Go to Symbolic Variables and add a new variable called IsFullDotnet4.  Then use Tarma’s support for symbolic expressions to read whether the registry key exists by setting the new variable’s value to this:

<$rkaccess(<HKLM>\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full)>

It should now look like this:

Adjust Prerequisites Condition

Go to the prerequisites section and adjust the condition to install the .Net 4 Runtime by setting the condition to this:

NOT IsFullDotnet4

It should look something like this:

That’s all you need – Tarma will now upgrade .Net 4 Client Profile installations to the Full version.

Replacing Strings in XPObject.SetPropertyValue with Lambdas

I came across a post on Aussie Alf’s blog today about removing magic strings from the persistent property setters in the XPO ORM from DevExpress. 

The Aussie Alf blog is written by Michael Proctor who is a member of the DevExpress community DXSquad, specialising in XPO.  The blog is a superb resource for any XPO developers and really worth reading.  Michael is also a very active member on the DevExpress forums and may well come to your help with an XPO issue there.

XPO uses a classic INotifyPropertyChanged pattern and passes a string of the changed property name into SetPropertyValue method.  You can see this below:  

1. public class Customer : XPObject
2. {
3.    private string _number;
4.    public string Number
5.    {
6.       get { return _number; }
7.       set { SetPropertyValue("Number", ref _number, value); }
8.    }
9. }

The problem with this approach is that the compiler can’t determine whether the string is correct or not, leaving you open to potential runtime errors.  Michael’s solution to this to generate a helper class that can be used in the property setter and he has a Visual Studio plugin that generates and refreshes the helper class for you based on your domain model. 

This is a great approach to the problem and you can read more about it on the homepage for Michael’s plugin, XPO_EasyFields.

Michael’s XPO_EasyFields plugin uses the free DXCore Visual Studio plugin from DevExpress.  Personally, I use Resharper and don’t have DXCore installed, so I thought I would share my approach to removing the magic strings - I use a helper class and lambdas to do this.  It looks like this:

1. public class Customer : XPObject
2. {
3.    private string _number;
4.    public string Number
5.    {
6.       get { return _number; }
7.       set { SetPropertyValue(Property<Customer>.Name(x => x.Number), ref _number, value); }
8.    }
9. }

This relies on the use of a generic Property class and a helper method that gleans the property name from a Linq Expression.  The property class looks like this:

1. public static class Property<T>
2. {
3.    public static string Name(Expression<Func<T, object>> expression)
4.    {
5.       if (expression == null) throw new ArgumentNullException("expression");
6.       if (expression.Body is MemberExpression) return ((MemberExpression)expression.Body).Member.Name;
7.  
8.       if (expression.Body is UnaryExpression && ((UnaryExpression)expression.Body).Operand is MemberExpression)
9.       {
10.          return ((MemberExpression)((UnaryExpression)expression.Body).Operand).Member.Name;
11.       }
12.  
13.       throw new ArgumentException(string.Format("Could not get property name from expression of type '{0}'",
14.                                                 expression.GetType()));
15.    }
16. }

The magic comes from translating the little lambda expression x => x.Name to a string.  If I remember right, I originally based this on some code from Jeremy Miller, but there are various implementations out there.  Here’s and elegant one from Paul Stovell that’s focused purely on INotifyPropertyChanged. 

As Paul mentions in the above link, it’s worth noting that there is a performance hit when using this approach.  Michael’s approach of generating the code does not have any performance hit.  You may need to consider the performance issue if you have very high rates of properties being set. 

I did some simple performance tests that show a 10-15x overhead with my approach compared to Michael’s.  However, this only becomes relevant with a very large number of property sets.  For my usage scenarios the added quality benefit outweighs the performance hit, but you will need to carefully consider your scenario.

Lastly, to take this further, and get an even tighter syntax, I add this helper method to my persistent classes:

1. protected void Set<T>(Expression<Func<Customer, object>> property, ref T holder, T value)
2. {
3.    SetPropertyValue(Property<Customer>.Name(property), ref holder, value);
4. }

This allows the setter to be even more compact:

1. private string _number;
2. public string Number
3. {
4.    get { return _number; }
5.    set { Set(x => x.Number, ref _number, value); }
6. }

The downside is that you need the helper method in each class.  Down to taste that really, but I always go for the tighter syntax wherever possible! 

You can get the code from bitbucket and browse the salient parts here.

Sometimes It Just Works

Some things in life that just do what they say they will do and when this happens you get blown away. 

VMware Workstation says it lets you use Visual Studio to debug an application that is running on a virtual machine.  I used this recently and was blown away by how easy it was to set up and by how amazingly useful it was.

The story is that I released a new build for informal testing, but it could not be installed.  I installed it onto a clean XP VM (yeah, I should have done that already…) and got the error myself.  However, there was no error information coming back from the application as the failure was happening before the logging layer was instantiated.

I was stuck.  I could reproduce, but had no other information to help.  Then I remembered that VMware Workstation had the facility to debug apps running on VMs.  So, I followed the instructions (yes, I was desperate enough to read the VMware help file!!) and set up a VM for remote debugging.  This was pretty swift to achieve and I then started a debugging session on the VM from Visual Studio. 

Almost immediately I could see what was happening: it was my bad – I’d just forgotten to include a third-party assembly with the build.  My dev box was happily loading it from the GAC and so I couldn’t see I’d missed anything.

VMware Workstation just did what it said it would do.  in doing so, it got me out of a sticky situation.  Also, it says it has the ability to record and replay a debugging session…maybe next time, eh?

In the meantime, and whilst loving the things that go right, here’s a shot of the error from VS debugging on the VM: