[FIXED] MVC Design - How many controllers?

Issue

Overview

I’m building a simple web application consisting of a canvas and elements on the canvas.

The canvas supports the following operations: load, save

The elements support the following operations: move, resize

JavaScript on the web page sends a message to the server for each operation and the server sends an appropriate response.

My design

Note: the arrow between the Canvas and Element objects is supposed to denote that the Canvas object contains a list of Element objects. I didn't have the right symbols for the diagram.

Example work flow

1. An element on the canvas is moved generating an element_moved message.
2. The front controller manages the session and passes the message to the canvas controller with the correct canvas object.
3. The canvas controller inspects the message and sees that it is for an element on the canvas and passes it on to the element controller.
4. The element controller parses the message and updates the appropriate element object directly.

Question

Is this hierarchical arrangement of controllers common place in MVC designs or am I completely missing the point? I've searched for several hours but haven't found any sites which discuss MVC design in more depth than simply returning a page view.

My motivation behind the design was that each object that the client needs to interact with has a controller so that if the interface changes (to support new methods) then the corresponding controller can be updated without impacting the other parts of the design.

Solution

usually you won't have one controller calling another in MVC. What you have specified as Element Controller is really just a part of business logic to update the canvas model. If your use case requires you to update the elements independently of the Canvas, then you will have a separate Element Controller, calling the business logic to update the element.

Cheers, Ryan

Answered By - ltfishie