我应该如何维护购物车以避免频繁前往服务器？

Question

My project in MVC is an order carting project. The carting is done with the following structure. There is an order object which holds:

cOrder -> List<cOrderItem>

cOrderItem-> List<dressing>, List<topping>, List<specialInst>

I am holding it in Session . Is it the right approach to hold it in Session without losing performance. Or should I follow an alternate approach?

Answer 1

I presume what you mean by "trips to the server" you really mean "trips to the DB" because whenever are dealing with the Session you are at the server anyway.

The Session will do the job, however, there are a couple of caveats that might be a problem

• Session is not persistent, it's all stored in memory. This means that there is the potential for you to lose the session at any point eg app pool recycle.
• Given it's not persistent, this means that a users cart is only maintained within a single session ie if the users session expires they will effectively lose their cart.

One approach which I have used in the past is to use a client-side cookie to maintain a basket session, this means

1. It's persistent storage so it's retained across sessions (not just a single session)
2. Nothing is stored on the server
3. It's very quick

There are a couple of small caveats with this approach as well

• Browsers need to have cookies enabled
• Users can clear their cookies (as such, losing their basket)

However, I've found that these issues are very rarely a problem as most people enable cookies in their browser and most users very rarely clear their cookies (and the chances of them doing it during a session is relatively low).

Answer 2

Yes and no. :)

Placing stuff that needs to survive across requests in the server session is fine for smaller websites, but it does limit scaling; it will be more difficult to distribute the load over multiple server machines, because either the session would need to be replicated to each machine, or all requests from a particular user would need to be routed to the same machine. There are out-of-the-box solutions for this however, it is not that big a deal.

But holding stuff in the session has other downsides. The session timeout for example will kill all the products that were in the cart if the user decides to for for lunch in the middle of his shopping spree.

Ideally, these days, I would be looking at storing the cart locally, in localStorage . Support for this is increasing rapidly. You would have some big advantages over storing it in the session:

1. Less memory needed on the server(s).
2. More scalable as there is no server state; each request may be routed to any server that has capacity at that moment.
3. No session timeouts killing your shopping cart.
4. Local code (Javascript) can access the shopping cart without having to make trips to the server and back.

Option 4 is becoming more important as of late. If you have your data available locally there are many things you can do with it later on that would be more difficult otherwise. Working offline for example could be done that way. You can fill your cart offline and only need to be connected to actually place the order with the webshop.