Applying context to a model...

I didn't attend QCon earlier this month, but I followed several attendees blogs and co-workers responses to the Eric Evans opening presentation. Alot of people mentioned the fact that Evans wished he'd dealed with 'Bounded Contexts' earlier in the book.

I'm now getting this feeling very much on my current assignment - over the last week we've had a great realisation that the application is a chameleon or if I'm feeling less generous a 'wolf in sheep's clothing...'

The minute you realise you've multiple different user types using your application you definitely have different 'Bounded Context's'- you could have users who care greatly how 'Orders' are modelled and the behaviour contained within, but you can also have other users who care nothing for how 'Orders' are modelled per say - typically I'm thinking of users who focus on reports etc.

This is not to say even if you have a single user you shouldn't give your model context within a certain area, I think a rule of thumb on this front is - if it's getting to difficult to add behaviour to the model may be it's time to break to the model apart into separate contexts. And remember it's not a bad thing to duplicate entities in different context's because more than likely they're not offering the same behaviour...

Do I think you can share entities between context's - 'Shared Kernel' springs to mind...

Comments

Implementing a busy indicator using a visual overlay in MVVM

This is a technique we use at work to lock the UI whilst some long running process is happening - preventing the user clicking on stuff whilst it's retrieving or rendering data. Now we could have done this by launching a child dialog window but that feels rather out of date and clumsy, we wanted a more modern pattern similar to the way <div> overlays are done on the web. Imagine we have the following simple WPF app and when 'Click' is pressed a busy waiting overlay is shown for the duration entered into the text box. What I'm interested in here is not the actual UI element of the busy indicator but how I go about getting this to show & hide from when using MVVM. The actual UI elements are the standard Busy Indicator coming from the WPF Toolkit : The XAML behind this window is very simple, the important part is the ViewHost. As you can see the ViewHost uses a ContentPresenter element which is bound to the view model, IMainViewModel, it contains 3 child v

Showing a message box from a ViewModel in MVVM

I was doing a code review with a client last week for a WPF app using MVVM and they asked ' How can I show a message from the ViewModel? '. What follows is how I would (and have) solved the problem in the past. When I hear the words ' show a message... ' I instantly think you mean show a transient modal message box that requires the user input before continuing ' with something else ' - once the user has interacted with the message box it will disappear. The following solution only applies to this scenario. The first solution is the easiest but is very wrong from a separation perspective. It violates the ideas behind the Model-View-Controller pattern because it places View concerns inside the ViewModel - the ViewModel now knows about the type of the View and specifically it knows how to show a message box window: The second approach addresses this concern by introducing the idea of messaging\events between the ViewModel and the View. In the example below

Custom AuthorizationHandler for SignalR Hubs

How to implement IAuthorizationRequirement for SignalR in Asp.Net Core v5.0 Been battling this for a couple of days, and eventually ended up raising an issue on Asp.Net Core gitHub to find the answer. Wanting to do some custom authorization on a SignalR Hub when the client makes a connection (Hub is created) and when an endpoint (Hub method) is called: I was assuming I could use the same Policy for both class & method attributes, but it ain't so - not because you can't, because you need the signatures to be different. Method implementation has a resource type of HubInnovationContext: I assumed class implementation would have a resource type of HubConnectionContext - client connects etc... This isn't the case, it's infact of type DefaultHttpContext . For me I don't even need that, it can be removed completely from the inheritence signature and override implementation. Only other thing to note, and this could be a biggy, is the ordering of the statements in th

Awkward Coder

Search This Blog