关于WCF类库和WCF应用程序托管的困惑

Question

I have a web site and would like to expose certain functionalities using WCF.

Before deciding which type of WCF project I need to use I wanted to compare the differences between WCF Class library and WCF application . I know this question has been asked many times and answered many times and the answers are usually about different hosting options each one offers but I wanted to try and see the differences, so this is what I tried:

Step 1 - In a same solution, I have created a WCF Service library project and created Client console app project, set the console app as a startup project, referenced the service library project from the client project and in the client console app I could instantiate the service and can consume the service methods. I didn't even add a service reference to the client project.

Step 2 - In a same solution, I have created a WCF Service application project and created Client console app project, set the console app as a startup project, referenced the service application project from the client project and in the client console app I could instantiate the service and can consume the service methods. I didn't even add a service reference to the client project.

On both steps after compiling the solutions I was able to copy the client app's exe and the service dll's to a different location and still be able to run the clients.

Based on this little excercie I am confused about the hosting part. It seems wether I use WCF Class library or WCF application type I get the same result.

This is just like using multiple projects in a solution, you reference one from another and use the methods, there must be something I am missing which highlights the differences between the two and highlights the benefits of using WCF, also in the past I remember I had to add a service reference to the clients apps in order to consume the service, why is this not the case here?

Thanks

Answer 1

1) Running a wcf service application allows you to provide communication into a single application, where you have a single instance of a thing you want to provide access to. Maybe this is a game, or a chat room without an external state engine or datastore. This is useful for providing diagnostic information about an application you might have written for example. I used this to provide external control for an industrial robot that I wanted to provide remote control access for.

That is to say, that you write an application, it has a function. You want to expose part of that functionality to remote applications. You do this by adding a WCF endpoint to your existing application, so your application itself is controlling the WCF hosting elements, lifecycle of the endpoint etc.

2) Running a WCF Service is for when you've got an external data store, or your service is stateless. A translation service, lookup service and web page requests fall into this category.

With a service class, you're saying here is this service, this thing that provides a function. It isn't tied to the lifecycle of another application or process and is typically hosted by IIS. IIS manages when the class is loaded and run based on the requests that come into it. These services have no internal persistence and rely on an external datastore, or are, by nature, stateless (think of a postcode lookup, or a calculator service)

It sounds like you're actually adding the projects as references, rather than connecting to them as services. That is to say, that the consuming application is actually loading the service as an assembly (in the same application/ memory space) rather than as a separate application/ service that your application then uses WCF to communicate with.

Answer 2

1. The WCF Service Application template can be used to create WCF services with a hosting website created within the project
2. The WCF Service Library template can be used to create WCF services that are hosted by the WCF Service Host , and these can be tested using the WCF service Test Client.

the biggest advantage of using a standalone library (apart from decoupling the logic) is that you can easily migrate your service, ie host it in another application or another type of application. Eg, let's say you're hosting your service using IIS - you can easily move your service to a standalone application, etc.