Ajden Towfeek

Towfeek Solutions AB

Entity Framework 6 Code First unreported breaking change/bug when migrating from version 5

Came a cross a nice bug in my golf score app on my season premiere round yesterday. I suddenly had a couple more strokes than I should with my HCP, although it seemed fair since it was the first round and all it didn't make sense. I hadn't made any (programmatic) changes to the code since the last time I played. 

It took me a while to figure it out but my strokes were based on the female slope. All the custom male and female slopes were suddenly flipped, how come? I had moved the site from surftown to windows azure and with that also upgraded EF from 5 to 6 and compiled the back-end for .NET 4.5 instead of 4.0.

Without diving into golf details a golf club has one to many courses and a course has one to many tees. How many strokes a player gets from a given tee is based his HCP and is usually calculated with a formula. Unless the course has a custom slope table, then you'll need to specify explicitly how many strokes you'll get for a given HCP. The latter is the case on my home course, which also is the reason for me creating the app, since there is no other app that handles this well.

So my entities looked something like this (yup, I'm serializing my EF POCOs directly in my WebApi service, get over it :D)

And since I haven't mapped up the inverse property EF won't be able to give the foreign keys good names, so the table will look like this:

which isn't neat but it's fine imho, it works, or at least it did work! Now all of the sudden CustomHcpAsMale and CustomHcpAsFemale switched places when getting the data. Since EF seemed to be confused I went ahead and explictly mapped the inverse properties, changing the code to something like this:

which after applying the migration changed the tables to look like this:

and voil√°, problem solved! Once again upgrading libraries to run the latest and greatest versions for no reason bites me in the ass. I'll try to report this to Microsoft as a breaking change, at least it was an easy fix and I figured it out quickly!

Lessons learned - don't be lazy like me when mapping navigation properties!

Hope it helps somebody out. Peace!

Lab days with focus on security (STS, WebApi, WCF and WIF)

Lab days once again at work, this time I focused on security. Can't share the code this time since it contains some company confidential stuff but the diagram below basically summarizes my architecture idea.

Securing WCF service with WIF

There are plenty of blogs out there descibing how to do this so I'm not going to explain this i depth, if you however only have experience with using WIF 3.5 as me I found an excellent migration guidelines page on msdn (http://msdn.microsoft.com/en-us/library/jj157089.aspx). We use a custom binding for tcp transport support with reliable sessions which makes you wanna kill yourself when you see the binding configuration. Due to this I can't share the code since it is considrered "intellectual property" of Saab (me?).

Important WIF 3.5 to 4.5 change!

You could previously access the calling users claims in the WCF service by casting ServiceSecurityContext.Current.PrimaryIdentity to ClaimsIdentity. This is no longer true, you'll get the claims by casting Thread.CurrentPrincipal to ClaimsPrincipal or Thread.CurrentPrincipal.Identity directly to ClaimsIdentity. For this to work you'll also need to set <serviceAuthorization principalPermissionMode="Always" /> on the service behavior declaration. See also Dominick Baiers post for more details.

JWT, Identity Server v2 and WebApi

I've updated our development STS in our product at work from startersts to identityserver v2, which I thought was a great platform to continue exploring, especially since it supported to issue JWT (json web tokens). At least I thought it did until I discovered that it doesn't! They do however have a branch that supports it and uses Microsoft JWT (https://github.com/thinktecture/Thinktecture.IdentityServer.v2/tree/Microsoft-JWT).

I found a nice message handler that validates JWTs which uses JSON Web Token Handler For the Microsoft .Net Framework 4.5 written by the security guru Vittorio Bertocci (http://code.msdn.microsoft.com/AAL-Native-Application-to-fd648dcf/sourcecode?fileId=62849&pathId=697488104). And as always I encountered major problems when trying to validate the JWT issued by identity server on the server-side (webapi). Victor uses windows azure ad together with Windows Azure Authentication Library which of course validates the token correctly.

I think there is a may release coming up for identity server, perhaps I'll give it another shot then, but for now I had to use Azure AD.

The outcome wasn't actually what I expected when I began but the road there was educative, I suggest following Victor on http://www.cloudidentity.com/blog to keep up with the updates on the json web token handler which currently only is in the developer preview stage. It hurts to keep up and always use bleeding edge technology but hey, they don't call it lab days for nothing. ;-)



WinRT app @ Labdays

Installed win8 on my work laptop not too long ago so I decided to create my first winrt app during lab days at work. Due to lack of imagination I created a simple dashboard app for our product SAFE (really ugly page on saabgroup btw).

Started of by looking at some sessions on channel9 and googled design patterns, frameworks and ended up with the following:

I ended up writing a custom navigation service that I bootstrapped on application startup to make the IOC container from MVVM Light play nicely together with the AlternativeFrame from WinRT Xaml Toolkit. If you pay attention to the navigation between pages you can notice the nice dissolve transition which is done in AppShell.xaml in only 4 lines of markup.
Once I got the basic architecture in place I noticed that the panorama control from windows phone was missing for winrt. One google search later I found a blog post that addressed this issue so I ended up copying some code since I didn't want to install the entire nuget package win8nl. What it basically does is to add a panorama behvior to the FlipView control. The sad thing though is that you can't flick the screen if you don't have a touch screen, which is extremely frustrating!
As for what goes for component arts data viz library I really think it's not worth to pay for (trial is free), in the short time I played around with it I stumbled upon several bugs. An ugly work around for the PieChart control can be seen in the code behind file MainPage.xaml.cs. When data binding to an observable collection the control goes bananas as items are added to the collection, I needed to reset the DataSource for each added item for it to work properly.
All and all I'm pretty satisfied with the choice to use MVVM Light together with WinRT Xaml toolkit and the custom navigation service, I will definitely reuse that part for other projects.
Anyways the result can be seen in the vid below, you can get the source code here, if you're interested in how I hooked up the components and architecture. You will probably not be able to run the application since it requires our back-end and I didn't spend too much time on exception handling.


Merry x-mas everybody and a happy new year, I'm off for two whole weeks!


Performance measurement ASP.NET MVC vs. WebAPI

I've been playing around with WebAPI for a couple of days now and I'm quite pleased with most of it so far. At work we have a stripped down a MVC3 site (threw away the M and the V) for ur public REST interface. Except for the ugly ActionResults in the controllers we are satisfied with it so far. I've read some articles on how the web api pipeline is supposed to be more optimized so I thought I'd put it up for a test before trying to sell in the platform upgrade to our product owners, also it would result in our first major version bump so we need to be sure that we can benefit from it and not just do it for the sake of fun (for me :-)).

The server side is a simple controller with 4 actions, 1 get, 1 post, 1 put and 1 delete method that only returns a status code, no I/O or business logic we just want to compare the pipelines. The test will run a five parallel threads executing 100 000 requests all together. The MVC site is hosted on a IIS 8 Express server and the WebAPI is both self hosted and hosted on a IIS8 Express server. The test was performed on my developer laptop running on Intel Core i7 CPU @ 2.67 (dual core with two threads on each CPU), 8GB RAM and 64 bit Win7 operating system.

 Avg. request time (ms)Total run time (s)Requests per second
MVC (IIS) 0.42 41.83 2391
WebAPI (IIS) 0.35 35.06 2852
WebAPI (Self Hosted) 0.12 11.67 8567


The results don't say much since the average request time is very fast in all three cases but a relative comparison shows that MVC vs. WebAPI on IIS is ~20% and the self hosted console application is a whole ~260% faster. Although this pure pipeline time will be negligible when adding business logic with I/O operations or even a single WCF call (~50ms perhaps?).

There's a whole lot more I could write about asp.net webapi but I'll save it for future blog posts and leave you with the performance measure for now. 

The code for the test is available for download here, please don't contact me about translating it to VB ;-)


Building real-time web app with SignalR

We just recently had lab days at work which for me basically means that I can play around with some new tech to keep myself up to date. Anywho, one of the things I tried out was SignalR which is a .net library for building real-time, multi-user interactive web applications.

To goal was to build a simple chat, textbook example, shouldn't be any fuzz, right? I started out with an asp.net mvc 3 empty project and installed the EntityFramework, SignalR and knockoutjs nuget packages. Lately I've been using knockoutjs pretty much in all my web projects, I'm a big fan!

PM> Install-Package EntityFramework
PM> Install-Package knockoutjs
PM> Install-Package SignalR

I'm not a big fan of entity framework code first but it was enough for my throw-it-away-when-you're-done requirements. The basic idea is to just create POCOs and decorate the properties with attributes and the db will be generated for you. 

The only entity I want to store is a chat message:

public class Message
    public int MessageId { get; set; }

    [Required, MaxLength(200)]
    public string Text { get; set; }

and the actual database context as 

public class DatabaseContext : DbContext
    public DbSet<Message> Messages { get; set; }

keeping it really simple, no relations at all. And let's not forget to register the initializer in Application_Start.

Database.SetInitializer(new DropCreateDatabaseIfModelChanges<DatabaseContext>());

Now to the fun part, SignalR. We simply create a Hub that runs on the server that will be able to invoke methods on our clients.

public class Messages : Hub
    public void GetAll() { ... }
    public bool Add(Message newMessage) { ... Clients.messageAdded(message); ... }

and on our page we only need to 1) create a proxy on the fly, 2) declare a function on the hub so the server can invoke it, 3) call on the add method on the server.

$(function () {
    // proxy created
    this.hub = $.connection.messages;

    // method invoked by the server when a message is added
    this.hub.messageAdded = function (m) { ... };

    // how we send a message to the server
    this.sendMessage = function () { ... this.hub.add(m); ... };

The server-side code is telling all the clients to call the messageAdded() JavaScript function. Mind blowing? We are actually calling the client back from the server by sending the name of the client method to call from the server via our connection. SignalR handles all the connection stuff on both client and server and makes sure the channel stays open and alive.

Screenshot of desktop browser and windows phone emulator browser:

Download the code (793,9KB) for full example.