Author: andersmalmgren

Abstract DI container Scopes

I saw an increasing demand for mini workflows / domain sub-parts in one of my projects. Most containers have some kind of support for sub scopes or nested containers, but I do not want to expose the Container API. If you have few places were you need nested containers you can implement this directly for your container of choice. An example of this is a container specific implementation of Web API’s IDependencyResolver. But in our case we had several different needs for scoped contexts near the domain. My solution was to abstract the context in a interface IScopedContext. (more…)

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Entity framework 6 and fluent mapping

If you google for EF and fluent mapping this is the first hit you get which is not strange since its the official MSDN page about fluent mapping in EF6.

They only discuss overriding the OnModelCreating method and configure the mapping inline in that method. And this is the most common way of dealing with fluent mapping out there in the community. But there is a much better and seperated way of doing it which MSDN fail to show.

System.Data.Entity.ModelConfiguration.EntityTypeConfiguration

This little class is your salvation when working with Fluent mapping in large enterprise systems. Implement it like. (more…)

MVC Custom errors, HTTP status codes and SecurityException

We use Windows Identity Foundation in my current project. WIF introduced the Claim based authorization in .NET 4.5 which is a welcomed addition since we were forced to use outdated tools like EnterpriseLibraries Rule authorization to achieve something similar before it.

Whenever a claim is not met WIF will throw a System.Security.SecurityException exception which will not play nicely with MVC Custom errors because it will render a status 500 instead of the correct status 403. This is not very user friendly since the user will think something is wrong instead of understanding that he or she needs to order additional privileges to access said part of the system.

The solution is really simple and I did not find it when googling, thus this blog post 😀 (more…)

Seperate KO View formating and ViewModel state

A normal scenario with Knockout is that you want date and number observables to be formatted to the current culture of the client, this is easily implemented in a Knockout extender, something like.

ko.extenders.numeric = function(observable, options) {
    var textValue = null;
    return ko.computed({
        write: function(value) {
            textValue = value;
            var parsed = Number.parseFloat(value);
            if(!isNaN(parsed)) {
                observable(parsed);
            } else {
                observable(null);
            }
        },
        read: function() {
            var value = observable();
            if(value == null) {
                return textValue;
            }

            return value.toLocaleString(); //This  can be replaced with for example the Globalize plugin 
        }
    });
};

Use it like

this.amount = ko.observable().extend({ numeric: true });

The problem with this approach is that the ViewModel will no longer work against numbers it will work against formatted strings, so this.amount() will return a string instead of a number. This is very bad practice in a View/ViewModel seperation stand point. (more…)

Implicit dependencies and ‘copy local’ fails to copy

A common scenario with .NET Solutions is that you have a Project, lets call it Project X, that have dependencies to a library without explicitly using it from code. You have a host project typically a Web or Windows client Project that uses Project X, even with copy local set Visual Studio will fail to load that implicit dependency and you will receive a Runtime error when trying to run the project.

One solution is to add this reference to the host project even if it does not have any direct dependency to the library. I think this is bad practice and will get very hard to maintain in a large project with lots of dependencies and assemblies.

A better solution that I use is to create a little helper method

static RepositoryBase() {
   Util.EnsureStaticReference<System.Data.Entity.SqlServer.SqlProviderServices>();
}

It should be called as close to the dependency as possible for readability. In above example I have a Repository base class which uses Entity framework. I call it from the static constructor.

The implementation of EnsureStaticReference looks like this

    public static class Util
    {
        public static void EnsureStaticReference<T>()
        {
            var dummy = typeof(T);
            if(dummy == null)
                throw new Exception("This code is used to ensure that the compiler will include assembly");
        }
    }

Single Page Application with Sub-routing

One of my colleagues is working on a Single Page Application, he asked me for help on a solid design for routing and specifically about sub-routing. Sub-routing in a SPA is complex, as an example when you click a link in a list you want that item to be presented in a modal window. If you close the modal window and press back in the history you want it to show again, and if you press forward you want it to close. I choose to attack this problem with an Event Aggregation approach, where changes to the route resulted in a change event being fired to any listener. (more…)

Wrap client side code in a Web Forms Control

I’m currently between assignments and in the meantime I’m helping fellow colleagues with a Web Forms system. They needed a Combobox for a requirement and after some googling I found out that there is none for free which suits their needs. I have created a Knockout enabled combo called Knockout.Combobox. I decided to take this client side combobox and wrap it in a Web Forms Control.
(more…)

Client – Server Event aggregation with Role Authorization

I’ve covered my SignalR Event aggregation library in an earlier post found here. That library has a Constraint API so that you can control which events a specific user should receive. It requires you to write one constraint handler for each type of event. But how about standard declarative Role Authorization?
(more…)

Client – server event aggregation with SignalR

Event aggregation is really a pattern i like, there is something elegant about firing events and subscribers can listen to them without knowing who fired them. This creates decoupled domains both in backends and frontends. At my latest customer we saw an increasing demand for pub / sub and immediate update. We fired events on the backend event bus and in the frontend we had SignalR Hubs that picked up the events and forwarded them to the clients. This caused duplicated and similar code both on the client and on the web server. I decided to create an abstraction layer between SignalR and the event aggregator. The result is a library called SignalR.EventAggregatorProxy

(more…)

MVVM with Excel and Caliburn.Micro

One of my colleagues needed to modernize a tool we had for Excel. He asked me for suggestions, since he knew I’m into modern UI development. I know very little about the Excel API but after some googling I found out that you are limited to Winforms. There is however a control in Winforms called ElementHost that let you host WPF elements in Winforms. This coupled with a custom Bootstrapper for CM will enable you to develop sleek MVVM tools in Excel.

The Boostrapper will act as an entry point for our Caliburn enabled app. It needs to inherit from BootstrapperBase rather than the standard generic base class Bootstrapper of TModel.

public class Bootstrapper<TModel> : BootstrapperBase
{
    private readonly StandardKernel kernel;

    public Bootstrapper(ElementHost host)
        : base(false)
    {
        kernel = new StandardKernel();

        Start();

        var model = kernel.Get<TModel>();
        var view = ViewLocator.LocateForModel(model, null, null);
        ViewModelBinder.Bind(model, view, null);

        host.Child = view;
    }

    protected override void Configure()
    {
        kernel.Bind<IWindowManager>().To<WindowManager>().InSingletonScope();
    }

    protected override object GetInstance(Type service, string key)
    {
        return kernel.Get(service);
    }

    protected override IEnumerable<object> GetAllInstances(Type service)
    {
        return kernel.GetAll(service);
    }
}

Its constructor takes the ElementHost as argument and then starts CM using the Start method on the base class. We need to hook up the ViewModel manually and its done like.

var model = kernel.Get<TModel>();
var view = ViewLocator.LocateForModel(model, null, null);
ViewModelBinder.Bind(model, view, null);

First we create the ViewModel using Ninject, this way any dependecies for that model will be injected by Ninject. Then we ask CM to locate the WPF view using its convention based helper class ViewLocator. After we get the view we Bind it to the model using another CM helper class called ViewModelBinder.

Last but not least, we need to hook up the WPF element to the Winforms ElementHost.

host.Child = view;

Embedded resources

Alan Rutter asked me how to load embedded resources like themes etc.
App.xaml wont load in a none WPF project so you need to-do this manually like

var dict = new ResourceDictionary {Source = new Uri("Resources.xaml", UriKind.Relative)};
var app = new System.Windows.Application(); //This will load Application.Current
Application.Current.Resources.MergedDictionaries.Add(dict);