More AutoTesting - Powershell extensions and addins

There is a nice library called PS-Eventing that makes the event handling a whole lot cleaner and generally a nicer experience. This post with the plugin is not a smaller and doesnt really do any else other than the last post except cleanly deregister the event, but is much more user friendly.
I think i will also post my code on gisthub as I am not and have not been at my real machine for so long... i miss it... sorry.
Heres the link : http://gist.github.com/632749

Auto test - Thanks Powershell

Im doing some funky Nunit stuff* at the moment and sometimes the ReSharper or TD.Net runner wont pick up my inner fixtures, the console runner however runs them just fine. Here is a PS script to have auto test running on build:


$Script:initialdir = "C:\myroot\"

$fsw = new-object system.io.filesystemwatcher
$fsw.Path = "c:\mysln\myproj\Bin\"
$fsw.EnableRaisingEvents = $true

$action = {
$filter = "*Tests*.dll"
$file = $Event.SourceEventArgs.FullPath
if($file -like $filter)
{
$nunit = "C:\3rdParty\NUnit-2.5.2\nunit-console"
$currentdate = get-date -format g
write-Host "Running Tests on $file $currentdate" -ForegroundColor Yellow
&"$nunit" /xml:$_.Name-testresult.xml $file
if($LastExitCode -ne 0)
{
WRITE-HOST "Test have failed for $file"-ForegroundColor RED
}
else
{
WRITE-HOST "Test have passed for $file"-ForegroundColor GREEN
}
#$null = Remove-Event $_.EventIdentifier
}
}

Register-ObjectEvent -InputObject $fsw -EventName Changed "FileChanged" -Action $action
Register-ObjectEvent -InputObject $fsw -EventName Created "FileCreated" -Action $action


Note that you will either have to explicit unregister your event handlers or kill powershell to get rid of the handlers. Cancel the watcher by hitting ctrl+c and then Unregister by runnning these lines

unregister-event "FileCreated"
unregister-event "FileChanged"


*The stuff we are doing is to do with inheritance and inner test fixtures to give us a BDD experience without the drama of the BDD frameworks, that personally I still dont like. We are still a fair way off the TDD experience of the Ruby kids.

Threading - I am on a Journey

Recently it has become more and more apparent that I had a crack in my understanding of a key aspect of not only the CLR but computing in general. No prizes for guessing that it was threading and the general parallel programming constructs that go along with it.
Now I am not a complete n00b in the threading world, I have written code that uses threads in client and server side but it was typically handing off a single task to a single thread and looking back it was probably pretty delicate and by now in need of some re-factoring love.
The first real kick in the pants was playing with my 8 core machine and never seeing all 8 core light up in the task manager. How wasteful... its like all the Aston Martins I see driving over Tower Bridge; what is the point?
Next major trigger for me was a computationally heavy project that I, up until recently, was working on. My colleagues and I knew that splitting up tasks could make or break this system, however given a distinct lack of human resources and not exactly compelling hardware, time was never allocated to fleshing out the best approach.
Well I am no longer at that job (its somewhat unfortunate as the project could have been epic had it not be butchered by red tape and ego's) so I have had time to scrub up on my threading knowledge... well I thought I would just be scrubbing up. Sometimes you just don't know how much you don't know.

So in an attempt to short cut any one else's learning curve on the wonderful world of threading and parallel programming in the .Net world here are some great places to get started.

As always C# in a Nutshell is a great place to start with anything C# related. I have both 3.0 and 4.0, Joe is a great author; IMO every C# developer should have the latest copy of this book on their desk.

Next up the deceptively good CLR via C#. This book looks like its going to be as much fun as having teeth pulled out however it is surprisingly good and dives deep in the areas you want and would expect. I read the 2nd edition however will be buying the 3rd as soon as I can find it.
Obviously these books are not completely dedicated to threading but they have some great chapters dedicated to it. If you are after a more in depth reference I have been recommend Joe Duffys book : Concurrent Programming On Windows

Next up is my favourite learning tool : Tekpub. There is a threading production under way, it only has 1 episode but it is great. As I have a yearly subscription it was a no-brainer. For me this was valuable as it has a bunch of code and a great visual comparison of auto and manual reset events, Semaphores and Mutexes. I highly recommend this video if these are confusing you at all.

For a more casual and much briefer talk on Threading in the pre .Net 4 days check out Jon Skeets articles . I have found the multiple angles these guys talk about the same topic good for bashing it into my head.

The piece that I am currently reading is the PnP new book Parallel Programming with Microsoft .NET that is also available as a hard copy book and eBook. Code snippets for the text are available here.

The last piece that is semi related is my reading of the Manning book Real-World Functional Programming. Although functional programming technically has no direct link to threading its basic tenants strongly support parallel programming and as such I have been endeavouring to improve my understanding and use of functional constructs where it is appropriate. So far the books is very good it is in F# and C# so it has bee a good (re)introduction to F# for me.

With all of the movement in not only hardware (hyper-threaded and multi-core processors) as well as architectures (Grid, Cloud, ESBs etc) and the software frameworks we use (.Net's TPL, Rx etc) and how we use them (i.e the movement towards functional programming in distributed/parallel systems) I think it is becoming very clear that as .Net developers we need to know how this stuff works, how we can use it and what it means for the systems we build and the users that use them.

As tempting as it may be to run off and just blindly use the new TPL I strongly urge you to get a good understanding of the history and the older APM practices, I am sure this will ensure you will make better choices when you write your next parallel task.
As for me I'm back to reading, I have a long way to go...

Getting started in Asp.Net

I recently met a guy who was new to town and had picked up a job doing development for a place that appeared to be moving towards Microsoft focused solutions meaning he was likely to move away from his LAMP (Linux, Apache, MySQL, PHP) background to a .Net/Sql Server environment.

I realised after talking to him that there are a lot of ways you could go wrong coming into the .Net realm from a LAMP/Java/Python/Ruby background and this post, although intend for him, is generic enough that it may save other web developers valuable time to get up and running, and producing valuable software using the M$ stack

Asp.Net

Asp.net is a different beast to the many other frameworks out there and you could spend years (and many have) learning all the ins and outs of the beast.
Dont.
I would highly recommend skipping WebForms all together as IMO it is a dead framework. I have been doing MS MVC for the last year and did MonoRail (an open source ASP MVC framework) on the side prior to that and I have never looked back. Some of the significant benefits are :

• Matches the way the web works (you explicitly work with http verbs)
• clean html
• easy to learn
• pluggable
• testable
• simple
• And finally, IMO, encourages better coding practices, which web forms simply does not.

I will assume you will trust me and accept that MVC is the way forward and I will go ahead and recommend how to start.

Asp.Net MVC in action
First port-of-call is to pick up this book. It will give you the no BS version of the truth and covers some third party tools that will help you along the way. There is a second edition on the way however if you are using VS 2008 then this books is for you anyway. Manning (the publisher) often have good discounts so register for emails or follow them on Twitter to know when promos are running.

TekPub : Build your own blog with MVC
Tekpub is one of my favourite resources at the moment. It is great value for money and video is an efficient way to learn new concepts. I had bought several series and now have the yearly membership and many of my colleagues have done the same. Go check out the BYOB which shows how Rob* built a blog in MVC. There are also MVC 2.0 and various other Asp.net series available. Buy one, buy a bunch or get a month or yearly subscription, go on, you know you want to ;)
*Rob was on the team that actually built Asp.net MVC

Asp.net
Yes the website is a good place to get lots of info too! There are lots of little articles and videos from from smart people who live and breathe this stuff. Just be aware that there is sometimes a very Microsoft slant to the information, not a bad thing but something to be aware of.

Next there is the Database

SQL Server

If you have a background in Oracle or MySql then picking up M$ Sql Server should be pretty easy. The standard practices apply e.g. dont run your web app as System Administrator. Nothing to really say here to be honest.


Joining the web and data world is your data access strategy

Linq2Sql or NHibernate

The 2 standout choices for new commers IMO are the light weight data acess strategy from Microsfot called Linq2Sql (pronounced "Link to Sequel", just dont ever write it like that) or the OpenSource and more heavy weight NHibernate. If you are from a Java background NH may be a good tool, if you are from a Rails background then Castle ActiveRecord (which sits on tope of NH) may even be a good idea. However for most Linq2Sql is probably the best bet when you are getting started and NH is the best if you are building up more complex domains. The caveat with NH is that there is a steep learning curve. If you are new to it then check out SharpArchitecture or one of the abstractions in the NHforge.com to help bootstrap yourself. If you have a simple domain or going to be building from the database up (i.e. create a database table and then the c# code to use it) Linq2Sql is a better fit anyway.

Tools

If you are playing with the M$ stack at home then you will most likely not want to shell out cash for the full blown enterprise versions of Visual studio and Sql Server. For this reason they have the express versions. I have only ever used the SQL express edition (which is great) so have no idea what VsExpress is like. In saying that if i did not have the full version of VS I probably would not be using .Net and just be doing rails/sinatra dev (but thats just me).
Assuming you are working with the full version at work then be sure to invest in the Resharper VS plug-in. Its not super cheap but the time it will save you will mean it will quickly pay for itself.

I terms of source control TFS is the M$ standard, but I personally don’t recommend it. I think tools like Git or even SVN are better tools that integrate better with other platforms/tools and are free. TFS however does more than source control, so if you are using make sure you use all the good ALM bug tracking bits etc

Extra links

Follow the team behind the framework, most importantly Scott Gu (all .net dev should read his blog) and Scott Hansleman. Mr Hanselman also has a good podcast called hanselminutes that is not Asp.Net specific but a good subscription nonetheless.
StackOverflow is a great QnA community place for lots of developer question. The are lots of .Net and Asp.Net people hanging out here so most of your initial question will most likely have already been answered. The site itslef is even built on top of Asp.Net MVC and Linq2Sql so you can see that this combination is a very real world and scalable solution.

If you are in Perth (like this person was) check out the Perth .Net Community of Practice and the Alt.Net lads that have monthly beers and discuss things that may or may not be from the Microsoft mother ship that affect .Net devs.

Perth Alt.Net - RavenDb

Last I did a "talk" on RavenDb at the Perth Alt.Net beers. I must say I was really stoked at the turn out. Lots of banter, comments, queries, theories and general discussion. I sincerely hope that everyone else enjoyed it as much as I did. I also felt that last night was moving closer to what I hope these events should be. These shouldn't be one-way dialogue. IMO the presenter is there to just start discussion and then it becomes a group affair, there should be lots of interjecting, lots of crowd participation. Last night there certainly was that and best of all it stay on track, we didn’t veer off into off-topic subjects (much) and I think the night was better for it.

I really do feel lucky to be in the company of some very smart people and i want to thank everyone for letting me bleat on and not give me too much grief for being woefully underprepared.

However I put it out there that the people who are comfortable enough to ask the hard questions (and there were a few), please take the reins, we want to hear from you! I’m a strong believe that you can learn as much about some from the questions they ask as the questions they answer and there were some gems last night.
Please contact Mike (@wolfbyte) or myself if you are thinking you may be interesting is starting a discussion, or even if you want to hear about stuff especially if it is edgy and possibly not suitable for the standard M$ .Net community of practice stream (Mitch wheat is the contact for that if you do have M$ specific stuff however). Any feedback is good. The hardest thing for organisers is trying to figure out what the crowd wants and as we nerds are not the most vocal people, making it even harder to run nerd events.

A further incentive is we now have sponsorship. If you get up and present you get swag, swag you want. I worked out since I have been back in Perth I have received several thousand bucks worth of cool stuff from presenting or attending various .Net events. It’s worthwhile getting involved!

Garry Stewart is up next time (in about 2 weeks) talking about light wieght IDEs, specifically VIm and letting go of our addiction that is Visual Studio.

One big note I also want to make. Take the talks for what they are. The whole under current of Alt.Net is "options". We need to be aware there are options. We are not saying you must throw away SQL and use RavenDB exclusively or Vi will replace Studio, we just want people to open their minds. If last nights talk got you thinking about how you could get you python web stck talking to cassandra, sweet, most of what we are talking about is concepts, if there is a tool involved, its just there because it facilitates a different way of thinking. Thats all.

See you next time :)

DDD eXchange 2010 - London

Un fortunately i dio not attend this event (which looked like an awesome event) however the Skills matter guys were good enough to post the videos of the event... sweeet!

DDD EXCHANGE 2010 - PODCASTS, SLIDES AND PICTURES

Thye have recorded all the DDD eXchange 2010 talks. The slides and podcasts can be viewed here:

• Keynote: DDD Emerging Themes of 2010 (Eric Evans)
• Architectural Innovation: CQRS (Udi Dahan)
• Architectural Innovation: Eventing, Event Sourcing (Greg Young)
• The 1st Parkbench Panel Discussion
  
• DDD Revelations and Misunderstanding: A Report from the Trenches (Ian Cooper)
• DDD, TDD, BDD (Gojko Adzic)
• Folding Together DDD & Agile (Eric Evans)
• The 2nd Parkbench Panel Discussion
  

You can also find some photos taken at the conference here.

Thanks SkillsMatter!

Test Fakes - Solving a Domain Entity Issue

Follow on from :Testing with Domain Driven Design

Background on the design in question

• We are using NHibernate for persistence on Oracle.
• We have service that accept command that are coarse grained and perform a clearly defined business function, they are not chatty services.
• We are using the notion of aggregate roots so all child objects are created and managed by the owning aggregate root. If you need to access the child it must be done via the AR
• The domain is relatively large and complex.

Background problem

We had issues where we were dealing with domain objects in test and getting problems with interrogating child collections. For example we sometimes need to be able to update a child of an aggregate root and we were using the id of the child (within our command object) to indicate which child to update. We are using a basic database identity field (oracle sequence) for setting the ids on all of our user defined entities.
Herein lies our problem;* In our test we create an aggregate root complete with child objects. We then want to test, for example, updating a child of the aggregate root via a DTO based command (i.e. using an id to define the child to update) and we run into issues when all of the child object have the same id of 0 as they are not persisted (it’s a unit test). Now this would never happen in real life. Why would you issue a command to update something that has not been persisted, how do you even know about that object?
The quick solution that I have seen used a lot is to set the ids of all of the domain objects prior to running the test. I don’t like this if you are doing this by exposing the ID setter on the domain object. This is opening up the API of our domain for testability and is potentially the start of a slippery slope in to a pit of hell. An easy way around this is to use fakes. These object are just child object of the domain objects in question that help expose stuff the domain shouldn’t; in this case the ID setter.
The other alternative is to set the id on creation of the fake so the setter of the id is not exposed. This can also work but it will mean your fake will always have an id set. For the situation I was in this was not suitable.

The end solution

All domain objects have a fake create for it. All of the fake implement an interface ISettableId. This interface is defined as below:

**CODE GOES HERE**

public interface ISettableId
{
    bool HasIdBeenSet();
    void SetId(TId id);
}

With an implementation example (its id type is and integer) :

public class FooFake : Foo, ISettableId
{
    public FooFake(string name, TypeRequiredForValidConstruction myDependecy)
    : base(name, myDependecy)
    {}
    public bool HasIdBeenSet()
    {
        return _id != 0;
    }
    public void SetId(int id)
    {
        _id = id;
    }
}

This mean we can now create fake objects and emulate persistence later by reflecting down the object graph and setting all of the ids. This is much faster than hitting the database and has proved to be a very valid exercise as we can now run tests again transient and persisted versions of the object graph without having a db connection.
One additional thing I should mention is that the creation of child object now must be exposed as a hook. For example when we create child objects I do not just new up to object and add it to a collection. I call a protected virtual method that creates the child object and then add that to the list. This allows my fake to override the return type that is added to the list so children can also be fakes. This has not increased the exposure of the domain but has now facilitate a hook to allow me to create fakes for my child collection.

Caveats:

Fakes should not include any logic. The fakes I am using only allow the setting of ids. The only logic they have is to check whether the id is set (this allows us to skip objects that have had their ids set when we walk the object graph and not go around in circles). The only other methods that are required is the overrides of the creation of child objects.
Other methods you may find in the fakes are builder methods. Instead of having big factories for creating test object you may choose to put the object creation closer to the owner by putting it in the fake class itself.

Summary

As I mentioned, we have a pretty large and complex domain we were running into issues where the difference between persisted and non persisted objects graphs was becoming problematic; using the fakes has allowed us to keep the domain clean and only as open as possible while allowing us to emulate persistence without the cost of hitting a database. Over all I’m pretty happy with the result.

*I’m sure there are other way to solve this higher level problem