Building E-commerce Sites with MVC

For those of us who have spent most of our careers building business applications, the prospect of creating an e-commerce storefront can be quite daunting. Not only do you have to deal with calculating tax, estimating shipping and accepting payments, but employees need a way to manage products, discounts and marketing content. Thankfully, there's an open source e-commerce solution written in Microsoft ASP.NET MVC named nopCommerce that provides all this functionality and much more.

I was so impressed by both the functionality and the underlying architecture that I've created a presentation which I believe will serve as a great introduction to MVC as well as a tutorial on developing custom storefronts using nopCommerce.

We start off with a brief overview of basic MVC concepts accompanied by examples within the nopCommerce code. This includes strongly typed Razor views, HTML helpers, jQuery ajax calls, and fluent validation.

Once everyone understands how the website works, we dive into the infrastructure by introducing WCF services, using a generic repository with Entity Framework (EF4) and LINQ, as well as Dependency Injection (DI) with Automapper.

If you'd like to schedule this talk for your local user group, either request me through INETA or contact me directly.

UPDATE 7/13/2013
Thanks to the CodeStock crew and everyone who packed the room for my talk. Y'all had some excellent questions and I invite anyone with additional questions to comment below or contact me directly. Also, don't forget to provide feedback so I can improve the talk for next time.

Click here to view the presentation slides.

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Great MVVM, WPF, SOA and EF4 Articles

I was asked to put together some links to articles that would help our IT department ramp up on some of the patterns and technologies we're using. By the time I was done with the email, I realized it might be of use to others outside our organization so part three of my MVVM with WPF series was born. There are many approaches and I highly recommend researching beyond this handful of articles, but for anyone not yet familiar with these concepts I hope they help.

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The Model-View-ViewModel (MVVM) pattern helps to cleanly separate the business and presentation logic of an application from its user interface (UI). This separation is key for testability, maintenance and scalability.

http://www.codeproject.com/Articles/66585/Comparison-of-Architecture-presentation-patterns-M

Here’s an introduction to MVVM which illustrates how it leverages WPF data binding and commands.

http://www.codeproject.com/Articles/165368/WPF-MVVM-Quick-Start-Tutorial

The main difference between what we’re proposing and how they define MVVM in the previous articles is, by using a convention-based framework such as Caliburn.Micro and events/commands to wire up the View and ViewModel, they are completely decoupled allowing for better testability and future scalability. The Caliburn.Micro wiki has a good introduction to the functionality it provides.

http://caliburnmicro.codeplex.com/wikipage?title=Introduction

This article gives a good introduction to Attribute Based Validation which allows us to keep validation logic down in the business layer and entities where it can then bubble up and be reflected in the UI.

http://www.codeproject.com/Articles/97564/Attributes-based-Validation-in-a-WPF-MVVM-Applicat

If there’s interest in going deeper, here’s an article on using a Service Oriented Architecture (SOA) to decouple service providers from consumers allowing for greater reuse and insulating the application from core business logic.

http://forums.trossenrobotics.com/tutorials/introduction-129/soa-using-c-and-wcf-2307/

Finally, a  series of articles outlining the use of a Generic Repository with Entity Framework 4 (EF4) to reduce the amount of plumbing that must be written and maintained for data access.

1. http://huyrua.wordpress.com/2010/07/13/entity-framework-4-poco-repository-and-specification-pattern/

2. http://huyrua.wordpress.com/2010/08/25/specification-pattern-in-entity-framework-4-revisited/

3. http://huyrua.wordpress.com/2010/12/16/entity-framework-4-poco-repository-and-specification-pattern-upgraded-to-ctp5/

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See also:

MVVM with WPF Series Part 1. Disconnected WPF Applications

MVVM with WPF Series Part 2. WPF MVVM with WinForms Controls

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Disconnected WPF Applications

I was recently tasked with presenting a plan to turn an existing WinForms program into an enterprise level application. They wanted to stick with a Windows client, but since each form would already need significant rework to extract the business logic, I suggested moving to WPF using the Model-View-ViewModel (MVVM) presentation pattern.

MVVM is basically a type of Model-View-Presenter (MVP) pattern that makes use of declarative bindings. State and logic are stored in the Presenter (ViewModel) which presents an abstract view of the UI with no knowledge of what View will implement it.

With the Presentation Layer taken care of, it was time to address the heart of the Application. The immediate need was for a smart client, however the solution was still very young and continually changing so it seemed a Service Oriented Architecture (SOA) would provide the most flexability and reuse. The question was how a disconnected client would use services.

Microsoft used to offer an application block for this specific purpose. The Disconnected Service Agent Application Block helped maintain a queue of web service requests while working disconnected (offline), then submit them to the server when it became available. Unfortunately, it is no longer being maintained and I have not found a suggested replacement. My guess is that they would encourage use of Sync Framework, which is designed to synchronize databases and files, but can use custom providers as well.

We're using Sync Framework to replicate data down to the client for offline use, but to utilize SOA and keep business logic/validation on the server we need a way of queuing web service calls and resolving any conflicts that occur. I'm currently in the process of researching whether a Sync Framework custom provider would be a good fit or if the old disconnected service agent application block would be a good starting point.

The existing relies very heavily on SQL stored procedures. Fortunately, Entity Framework (EF4) supports calling the existing stored procedures so they wont all have to be rewritten immediately. The plan is to gradually move business logic up into the application layer and use entity model. I've also added a generic repository to allow mocking.

I welcome feedback and suggestions. If you've tinkered with custom providers for Sync Framework or have suggestions for how to best queue and resolve service calls I'd love to hear from you, either by leaving a comment below or on twitter (@gainesk).

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Using ODAC with EF4 via WCF

Oracle Data Access Components (ODAC) 11.2 Release 4 (11.2.0.3.0) with Oracle Developer Tools for Visual Studio includes support for Entity Framework and LINQ. Implementation is simple, however when I called the query from a WCF service I got the error:

System.ArgumentException was unhandled by user code
  Message=The specified store provider cannot be found in the configuration, or is not valid.
  Source=System.Data.Entity
  StackTrace:
       at System.Data.EntityClient.EntityConnection.GetFactory(String providerString)
       at System.Data.EntityClient.EntityConnection.ChangeConnectionString(String newConnectionString)
       at System.Data.Objects.ObjectContext..ctor(String connectionString, String defaultContainerName)
       ...
  InnerException: System.ArgumentException
       Message=Unable to find the requested .Net Framework Data Provider.  It may not be installed.

A bit of research discovered that 32-Bit Applications are disabled by default in the IIS Application Pool. As soon as I changed Enable 32-Bit Applications to True everything worked fine.

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