用于业务和数据层的 WCF 主机

Question

I checked alot of multi tier application guides and none talked about how to use wcf to host the layers.Im planning to make a test project and ill have a presentation layer/business layer/data layer along with the business objects which are classes generated automatically by EF (database first).

Question is, in real world, would the business layer and data layer each be accessed by way of a wcf host aka 2 hosts? or only 1 host?

1 between data and business layer 1 between business and presenation layer

Answer 1

Just for clarity,

A Layer could be just another project but on the same box.

A Tier is the physical separation of the code on separate servers.

Whether you are using layers or tiers or a mix of them depends on the needs. When I was working at a medical based company that also handled payment information they were shooting for a high level of PCI compliance so we had various tiers.

My [brackets] are physical barriers such as servers and routers.

[Front end -> MVC] -> [Firewall] -> [WCF -> Business layer servers] -> [Firewall] -> [WCF -> Database access] -> [Databases]

They also had another set of tiers to handle the PCI data specifically that branched from the business tier.

Would this be ideal for your situation? It really depends on the requirements of the project. If your data doesn't need to be highly secure then you could stick with just using layers instead. If you plan on having a few front-end components like mobile platforms and websites then you could shoot for..

[Front end -> MVC] -> [WCF/WebAPI -> Business Layer -> Data access Layer] -> [Database]

That would allow you to have multiple front ends to work with while sharing a common business layer and data. Again it is all depending on what your needs are. I hope this helped.

EDIT: Security is not the only reason for having tiers, accessibility and performance is another. If you are a heavy hitting application having multiple tiers with server farms utilizing them would allow for a few advantages. If your business layer is in a server farm of 30 servers you would have wide bandwidth and more processing power. These tiers could be distributed across the country or the world and have rules setup so users access the closest servers to them. There are a bunch of considerations when developing for tiers, starting out with layers will allow you to physically separate them into tiers at a later time if the demand comes for it. If you design the code well the move would be adding the additional service layer WCF/WebAPI to the tier to allow it to access the separated layer and then updating the calling end to use the service instead of the assembly directly.

Answer 2

Typically, you only host the business logic. If you host both the business and the data access layer, you'd have 3 network hops on each action: Presentation to Business to Data Access to Database. Each transfer over the network takes some time, so the less hops you have the better your application performs.

From an architectural point of view, the most important thing is to split the functionality of the application in layers that each serve a specific purpose (separation of concerns). However, the infrastructure view is a different one, so this does not mean that each layer does have to be hosted on a server. If you have a small intranet application, it might be enough to just split the application in layers and run all of them in the UI process. If the requirements change, you can layout the layers in a different way later easily.