What role does MVVM play in ASP.NET MVC 4 web applications?

Question

While I\'m reading the book \"ASP.NET MVC 4\" I\'m wondering about MVVM. I started googling and cannot find any books about developing web applications using MVVM, so I must be

Answer 1

Does that mean, the concept of MVVM / data binding just does not apply to client-server web applications?

No, you can apply the MVVM pattern to client-server web applications.

In fact Asp.Net MVC actually kind of does use this pattern - when the controller creates the view, it can pass in a "view-model". This view-model is often a POCO data object with all the data that a particular view needs, drawn from the model (database). The view uses this data to render the html page.

MVVM on wikipedia says it was introduced by Microsoft with WPF. Specifically, the view binds to properties on the view-model. The view-model then maps this to the database. By this definition then, Asp.Net does not exactly match that. Client-side frameworks like knockout.js and vue.js do support this kind of 2-way binding with view-model properties.

All these patterns are based on the fantastic MV* pattern. It was originally called the MVC design pattern. So this is the exact same pattern as Asp.Net MVC then? Actually, not quite. Controller means something completely different to start with (see MVC on wikipedia). The original MVC controller handles all user input directly not via the view. Second, the original MVC pattern was designed for a desktop app GUI and Asp.Net MVC adapted the pattern for use in a client-server web app. An ASP.Net controller is a collection of http end-points which the client-side html page can hit (eg form-post, page-navigation, ajax).

So there are a lot of M-something-V patterns and the general pattern is often called the MVC design pattern.

There's one more important wrinkle: client-side vs server-side. We've introduced rich client-side javascript frameworks and the fantastic MV* pattern is great here too. So now we could have something like: client-side View-Model-ServerHTTPEndPoints and server-side ServerHTTPEndPoints-ServerModel. The server-endpoints refers to Asp.Net controllers or the equivalent in whatever web framework or programming language you are using. From the server-side point of view, the entire client-side html is the view. The client-side model talks to the server ajax api (http endpoints) to sync data or trigger advanced actions. The ServerModel is normally a database. In knockout/vue, instead of client-side "Model", it would be ViewModel. If you use react/vue with redux/flux then the client-side would be View-ViewModel-Model-ServerHTTPEndPoints where the Model would be the redux/flux Stores. Also, often on the server-side, a service is introduced: ServerHTTPEndPoints-Service-Model. This way unit tests can hit the service directly rather than firing up the entire web server and making HTTP connections.