Auditing user actions

I want to be able audit user actions on the domain model - I want to track when & what they've changed. Now I can do this at the course grained level using nHibernate event listeners, they can tell me when an entity is loaded, saved, updated etc. But without interrogating the state of the entity in depth I'm unable to determine what's gone on between loading an entity and it being saved.

This is where the idea of domain events comes the rescue - the idea of generating events from the domain model. Now this could be done using the standard .Net event pattern, but as described in the above link the use of a decoupled domain events is way more powerful -the use of an intermediary ('DomainEvents' class) to decouple the domain model from the event handlers is simplistic and beautiful.

So now I can have an auditing service listening to both nHibernate & the domain model to track user actions across the domain and when a domain entity is persisted I can then push out the audit data to a message queue for processing asynchronously.

My requirement for auditing goes further than just tracking what a user did, it also includes tracking usage (of the domain model) - we want to track every time a user accesses content to provide usage reports and invoice accordingly...

This will be collected via the same domain events - it's just another specific audit handler, etc.

Simple!

Awkward Coder

Comments

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

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

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