WCF Interview questions--Part1

Basic WCF Interview Questions

What is WCF?
WCF stands for Windows Communication Foundation (WCF) and is considered as the Microsoft Service-Oriented Architecture (SOA) platform for building distributed and interoperable applications. WCF unifies ASMX, Remoting, and Enterprise Services stacks and provides a single programming model. WCF services are interoperable and supports all the core Web services standards. WCF services also provide extension points to quickly adapt to new protocols and updates and integrates very easily with the earlier microsoft technologies like Enterprise Services, COM and MSMQ.

What is the version of the .NET framework in which WCF is released?

WCF - Windows Communication Foundation is released as part of .NET Framework 3.0. WPF (Windows Presentation Foundation), WF (Workflow Foundation) and Card Space are also part of .NET Framework 3.0.
What is the advantage of using WCF over other distributed programming models like Web Services(ASMX), .NET Remoting, Enterprise Services stack etc.?

To understand the advantage of using WCF over other distribtuted programming models like Web Services(ASMX), .NET Remoting, Enterprise Services stack etc, let's consider the following scenario. We have developed an application using web services. As we know web services use HTTP protocl and XML SOAP formatted messages, they are good for developing interoperable applications in a heterogeniuos environment. We have a new client. Our new client is using .NET and he wants binary formmatted messages over TCP protocol, because interoperability is not a concern and binary formmatted messages over TCP protocol are much faster than XML SOAP formmatted messages over HTTP. To satisfy the requirement of this client, now we cannot use our existing web service. So, we have to develop a brand new remoting application from the scratch. The business functionality is the same in web services and remoting application. Since our different clients have different requirements, we ended up creating the same business application using web services and remoting technologies. This approach has several disadvantages as listed below.

1. Developers have to be familiar with two different technologies (Web Services and Remoting).
2. We end up creating duplicate business applications with different technologies which also leads to maintainance overhead.

On the other hand WCF unifies Web Services, .NET Remoting, and Enterprise Services stacks under one roof. For the same requirement that we have seen untill now, we just create one application and expose multiple end points to satisfy the requirements of multiple clients. In WCF configuration drives protocol choices, messaging formats, process allocation, etc. WCF services are loosely coupled, meaning that a WCF service is not bound to a particular protocol, encoding format, or hosting environment. Everything is configurable.

Why are WCF Services are considered as loosely coupled?

WCF Services are considered as loosely coupled because WCF services are not tightly bound to a particular protocol, encoding format, or hosting environment. All of these are configurable. At the time of designing WCF services, we donot have to worry about what protocol, encoding format, or hosting environment to use to expose the service. We can worry about all these at the time of deployment.

What are the 3 things that a WCF Services end point must have?

  OR
What are the ABC of a WCF service?

Address - The address where the WCF Service is hosted.

Binding - The binding that decides the protocol, message encoding and security to use. Binding also decides whether to use reliable messaging and transaction support.
Contract - The service contract defines what service operations are available to the client for consumption.
So the Address(A), Binding(B) and Contract(C) are called as the ABC of the service end point.

What is the role of WSDL in WCF?

OR
What is WSDL?
WSDL stands for Web Service Description Language. The WCF service exposes the WSDL document for the clients, to generate proxies and the configuration file. The WSDL file provides the following information for the consumers of the WCF service.

1. Provides the information about the service contract and operations available.
2. Provides the information about all the end points exposed by the WCF service.
3. Provides the information about the messages and types that can be exchanged between the client and the WCF service.
4. WSDL also provides any information about the policies used.

What is the tool that a client application can use to generate the proxy for a WCF service?

Service Utility (svcutil.exe) can be used by the clients to generate the proxy and configuration file. For the client to be able to generate proxies, the service should enable metadata exchange.

WCF Interview Questions on Contracts - Part 1

Define Service Contracts and Operation Contracts in WCF?
1.       Service Contract - An interface that exposes the service operations is usually decorated with the service contract attribute. Always provide meaningful Namespace and Name to a service contract as shown in the example below.
2.       Operation Contract - All methods in a service contract should have OperationContract attribute. You can also provide explicit Name, Action and ReplyAction as shown in the example below.
3.       Can you apply, ServiceContract attribute to a class rather than an interface in WCF?
4.       Yes, a ServiceContract attribute can be applied either to a class or an interface, but defining service contracts using interfaces rather classes has the following benifits.
                                                   1. Defining service contracts using interfaces, removes coupling to service implementation. Later the implementation can be changed at will without affecting the clients.
                                                    2. Defining service contracts using interfaces, also allows a service to implement more than 1 contract.
5.   What is the purpose of MessageParameter attribute in WCF?
6.   MessageParameter attribute is used to control the parameter and returned object names from a service operation. Consider the example below. On the service side, the method parameter name in SaveCustomer([MessageParameter(Name = "Customer")] Customer cust) is cust. If we donot use MessageParameter attribute, then "cust" is what is exposed as parameter name to the client, which is not very proffesional. So we are using MessageParameter attribute to expose the method parameter name as Cutomer.