WCF by Example - Introduction

		Chapter I

Latest modifications 

The last article added to the series is WCF by Example - Chapter XIV - Validation & Exception Management, this article was added early Jan 2011 and discusses how to implement the IDataErrorInfo interface in combination with Validation attributes. This approach provides a comprehensive validation mechanism that works both in the client and server side. The article also discusses exception and warning management.

Recently, a re-factor of the client services components have taken place reducing the number of required artifacts in the client side when a new contract is created or methods are added or amended. The code is already on Codeplex on the trunk branch. Existing articles will need revision as result of these changes, code at the branches will also require changes.

In Dec 2010, the server side of the application was deployed to Azure, a ready-to-run client is available on codeplex. The WPF client can invoke methods to a WebRole deployed in Azure. This source code can be found at CodePlex at eDirectory.WPFClient.Azure.zip

You may want to follow series/code updates at: @enriquealbert/wcfbyexample

Introduction

This article is the first of a series that discusses how to design and develop a WPF client using WCF for communication and NHibernate for persistence purposes.

Designing enterprise applications requires a comprehensive set of skills. In small and medium projects allocation of time and resources could be not feasible to the extent that is in larger projects, it is at this time where a source for best practices and patterns can become very beneficial. There are plenty articles, books and other materials covering specific aspects but it is almost impossible to find a single place where all the technologies and patterns are used in conjunction providing a comprehensive discussion of the why and how.

The intention of these articles is to provide an example of how a full enterprise application is developed from the early stages to a full functional stage. The articles build on top of each other where new aspects are covered or/and existing functionality is enhanced as a result of aligning the architect to the business non-functional requirements.

It is assumed in the series that Agile practices are followed so the solution's architect focuses in providing flexible mechanisms for RAD, DDD and TDD methodologies. One key aspect of the architect is the requirement to be able to deploy a full-functional client for business exploration purposes that requires a minimum infrastructure footprint; avoiding databases, deployment to IIS and so on. 

Background 

The architect requirements are as follow: 

• Rich client using WPF  
• Client connects to server using WCF services  
• NHibernate is used for persistence purposes  
• Client application can be run against in-memory repositories (Exploration Client)
• Deployment of the exploration client must be kept simple  
• The application must be easily testable, tests can be run against in-memory or NHibernate repositories  

Other assumptions: 

• We have full control over the client and server components
• We are creating the database from scratch, we are not using some legacy database
• We are deploying the server components using IIS7 and WAS; we will use TCP/IP
• We have full design control over the PK in the database tables, we will using unique long fields for all our entities in this project

The eDirectory solution

We are going to start using a very simple business scenario in our series, the focus on the series is the architecture not the business domain. We may extend our domain in the future if we find that we want to explore some more complex architect concepts. 

The business domain is based in a simple list of contacts, it is currently so simple that one single entity is only required: Customer. The solution name is eDirectory. 

The source code can be found at codeplex: WCF by Example  

The latest version can be found at the trunk branch, each chapter is located at its own tag branch. You may want to use the browse function within Codeplex to navigate among the branches. 

Architect Overview 

The eDirectory application defines three well differentiated application components: the database, server and client. 

Within the client and server the application is structured into layers, in most cases the layers are stacked one beside each other, continuous layers are provided with decoupled mechanisms so different implementations can be used. Some services are available across multiple layers.

As we earlier mentioned, we have full control of the clients and server. So we will not relay on late service discovery, instead the service contracts are available at both sides of the application. This is also true for the DTOs and some common business validation. As a result, a Common assembly is defined that contains components shared by the server and client applications.  

In the server side we find the core components, the business domain declares the business entities and their behavior (action methods). Then services are declared that exposes our domain action methods. The services for persistence and serialisation constraints only expose DTOs between the client and server. As a result, the transformation of entities to DTOs needs to be addressed in a comprehensive manner.  

In order to decouple our business domain from the database, the repository components are responsible for the persistence of our entities. We will define a generic interface between these two layers. Two concrete implementations of the repositories are available: in-memory and NHibernate. 

The transaction manager is our "unit of work" implementation. It is responsible for our business transactions and the handling of business messages (warnings and exceptions).

Finally, but not the least, we have the client components. The client is a WPF application designed using the MVVM pattern. This pattern provides a neat view XAML component with none or very little code behind, the binding capabilities of XAML in conjunction with the ViewModel class leverages how the client renders the DTOs provided by the services layers.

The client decouples the service layers into two main components. The adapter is responsible for the managing of business messages retrieved during the execution of services. The WCF Proxy layer is responsible for the management of WCF services, the design is neat and is a nice way of decoupling the client from the WCF service.

Available articles in Codeproject

Available chapters (source code) in Codeplex

Future chapters

History

14 June 2010 - Introduction article was created.
28 June 2010 - Chapter I is done and series are published.
05 July 2010 - Chapter II was added to the series
10 July 2010 - Chapter III was added to the series
16 July 2010 - Chapter IV was added to the series
23 July 2010 - Chapter V was added to the series
31 August 2010 - Chapter VI was added to the series
04 September 2010 - Chapter VII was added to the series
15 September 2010 - Chapter VIII was added to the series
19 September 2010 - Chapter IX was added to the series
07 October 2010 - Source code for Chapter XII is available at CodePlex
16 October 2010 - Chapter X was added to the series
04 November 2010 - Chapter XI was added to the series
24 November 2010 - Chapter XII was added to the series
12 December 2010 - In-memory WebRole is deployed to MS Azure
19 December 2010 - Chapter XIII was added to the series
07 January 2011 - Chapter XIV was added to the series
09 February 2011 - Chapter XIV section 2 was added to the series
07 October 2011 - Client re-factor was made available on Codeplex

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)