elements of ddd with asp.net mvc & entity framework code first v2

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Elements of DDD with ASP.NET MVC &

Entity Framework Code First Gabriel ENEA, Technical Director

MAXCODE.nl

Co-founder Joobs.ro – the first IT job portal in Romania

CodeCamp member / Iași [email protected] / gabrielenea.blogspot.com / @dotnet18


IT Camp 2011

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Agenda

# Unit Testing challenges

# Today Architectural Design

# New approach: Domain-Driven-Design

# Today’s Tools (@web)

# Demo

• Q&A


DEMO

Application requirements


UNIT TESTING CHALLENGES


How do you test it?


Testing on components


How do you start building an application architecture?

Focus on?

• building an architecture from scratch

• thinking about how to achieve unit testing

• start with modeling the database schema and data relations

• using drag & drop programming

• modeling the domain entities, relations, business rules

• reusing existing code?

• but, in the end, do you achieve 99,99% test code coverage?


Is unit testing achievable? 100%?

Yes or No? Who knows?

Maybe not! Possible answers:

• The customer doesn't understand this need

• Neither the management staff

• Instead, everyone expects you to write the perfect code

• As developers, every time we say: we need time to do it right!

• But, do we need time or we don't know how to achieve it?


TODAY ARCHITECTURAL DESIGN


Let's start thinking to architecture design

What? Right, now!?

Hey, we have only 1 hour to finish this presentation!

Indeed, but let's try to do something!


What stops 100% unit testing?

1. Layers

– How do we design them?

2. Business rules

– Where and how do we implement?

3. Persistence

– Should we use an ORM?

…


1 - Layers

Data Access

Business

Presentation


Data Access

Business

Presentation

1 - Layers – any problems?

Layers Coupling!

A strong coupling conducts to a hard way to do:

– unit testing

– refactoring

– agile development

– or be opened for changes


2 - Business rules

Where should these be located?

– Database

– Business layer

– User Interface (aka code behind!)

How do we test them?

– Running the application

– Automatically, maybe using unit tests

– Or we should let the customer test them!?


And...what's inappropriate here?

// somewhere in the business layer

public class Patient {

public DateTime Birthdate { get; set; }

public int Age { // computed value

get {

return DateTime.Now.Year - this.Birthdate.Year;

}

}

public bool IsAdult { // business rule

get {

return this.Age >= 18;

}

}

...

Strong coupling!


3 - Persistence

Requirements

• Persistence Ignorance / POCO

• Help Domain Model stay out of infrastructure stuff

• Decide where to store data (NoSQL?)

• Use code generation or an Object Relation (O/R) Mapper – Metadata mapping

• Support for the Unit of Work pattern


NEW APPROACH: DDD


Let's start with a new approach... Domain-Driven-Design

• What is Domain?

A new default architecture where:

• the database is not the first focus

• the layers are loosely coupled

• the business rules are within the application Domain

• it is easier to achieve unit testing

• Why? Today we have the tools!


A new default architecture - DDD


Building blocks of DDD


TODAY'S TOOLS


Today's tools (from a web developer perspective)

Dependency Injection frameworks

– Manage dependencies

– Castle Windsor, StructureMap, Spring.NET, Unity, ...

ASP.NET MVC 3

– a mature web development platform based on MVC pattern

Entity Framework 4.1 Code First / NHibernate

– helps you focus on your domain


What is Dependency Injection?

• = DI.Equals(IoC); // true or false?

• IoC = Inversion of Control

• DI = Dependency Injection

• Helps you to decouple the application dependencies

– Logging mechanisms (log4net, Enterprise Library Logging Application Block, ...)

– Persistence mechanism (direct access to database, ORM)

– User Interface dependencies on Domain services

– Layers


Dependency Injection

PatientService

Log4netLogger

PatientRepositoy


Dependency Injection

Builder PatientService

Log4netLogger

ILogger

3) uses 2) inject dependencies

1) creates


ASP.NET MVC 3 and DI support

• Based on MVC pattern

• Provides better support for IoC – Views/Controllers

• Model Validation support

• Check IDependencyResolver interface – simplify service location and dependency resolution

TService GetService<TService>() { … }

IEnumerable<TService> GetServices<TService>() { … }


Persistance with EF 4.1 CodeFirst

1st version benefits:

• CodeFirst development

• Better POCO support

• Mapping based on predefined conventions

(Convention over configuration)

• Fluent API for manual mapping entities to tables, no more .edmx files

• Built-in Model-Level Validation

• Dynamic database creation and dropping


DEMO

DDD architecture with ASP.NET MVC 3, Unity, Entity Framework CodeFirst 4.1


Conclusions

Focus on

– Analyze application dependencies

– Business rules

– Do refactoring!

– Design your Domain

– Don’t forget to do Unit testing


Resources

Books

• Domain-Driven Design, Tackling Complexity in the Heart of Software, by Eric Evans

• Applying Domain-Driven Design and Patterns, With Examples in C# and .NET, by Jimmy Nilsson

Online resources

• http://domaindrivendesign.org/

• http://www.infoq.com/minibooks/domain-driven-design-quickly

http://domaindrivendesign.org/



http://www.infoq.com/minibooks/domain-driven-design-quickly









Q&A

Elements of DDD with ASP.NET MVC & Entity Framework Code First


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elements of ddd with asp.net mvc & entity framework code first v2

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