在C＃中管理对象依赖关系的设计模式

Question

I m building a website in ASP.NET MVC 4 C#. Requirement is as follows: 0. Build an order by collecting required details across several pages.

1. User should be able to navigate back and forth (to check the values entered) before submitting the order finally.

2. There may be a dependency wrt data collected in subsequent pages based on the current selection. For example, if I change the country to which product needs to be shipped, custom duties & taxes applicable in the next page needs to be changed. Hence data in subsequent pages need to be invalidated. If modification to a field does not impact any other data(change in quantities ordered), current selection needs to be persisted.

For scenario 1, I m planning to use Memento pattern. The object will be serialized and persisted in database. However, I m not sure how to deal with scenario 2. I m sure there would be a design pattern that I can use here. A code sample would be definitely helpful.

Initially I thought of Observer pattern. However, I do not have any subscribers active to be acted on the change.(Values will be saved in DB and will be loaded of next/previous page). Also, we are mostly looking at a single entity of storage here (Field 1 and 2 will be populated on page 1, field 3,4,5 in page2......etc)

Answer 1

I would separate the responsibilities like this for your scenarios: 1. managing the page navigation and interactions 2. awareness of state of the object

Because you are going to have a complex page navigation based on your scenario, I would recommend you to use a Mediator to manage the interaction/communication between pages. In the other hand you need to somehow manage the state of the object and based on that state you would need to invalidate and take action, so you also would need to have a State pattern.

After this, there is one level upper that has the knowledge about what the scenario is that you can use something like usecase/application controller that manages your scenario using those implemented patterns (Mediator, State).