Elements of DDD with ASP.NET MVC & Entity Framework Code First v2

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
gabriel.enea@maxcode.ro / gabrielenea.blogspot.com / @dotnet18

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Agenda
# Unit Testing challenges
# Today Architectural Design
# New approach: Domain-Driven-Design
# Today’s Tools (@web)
# Demo

• Q&A


Application requirements

DEMO


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

Presentation

Business

Data Access


1 - Layers – any problems?
Presentation

Business

Layers Coupling! Data Access

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;
}
Strong coupling!
}

public bool IsAdult { // business rule
get {
return this.Age >= 18;
}
}
...


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

Log4netLogger

PatientService

PatientRepositoy


Dependency Injection
1) creates
Builder PatientService

Log4netLogger
2) inject dependencies 3) uses

ILogger


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


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

DEMO


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/domai
n-driven-design-quickly


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

Q&A


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Elements of DDD with ASP.NET MVC & Entity Framework Code First v2

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