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Developing core-business applications with DDDJimmy Nilsson, factor10
DEV-B311
About meDeveloper/architectjimmynilsson.com/blog
Twitter: @JimmyNilsson
Author”Applying Domain-Driven Design and Patterns” and”.NET Enterprise Design”
CompanyCo-founder and CEO for factor10
Context
Exponential effect!
Dare to challenge!TDomain-Driven Design (DDD)
How we as humans/developers are
Why Domain-Driven Design?Latest and trendiest?A template in Visual Studio?The best best practice?
No! Much better!
I believe that DDD can help very much in creating business value.
What is software development all about? $Why?
What?
How?
”Code!”
? ? ? And so on…
$
Basic software economics
Complexity
Productivity
Question is, is it essential complexity or accidental complexity?
Not just code in control
...the size is of tremendous importance!
The size…- drives cost- drives bugs- drives delays- drives team size, which drives code size…
What is Domain-Driven Design?Domain-Driven Design is an approach to the
development of complex software in which we:
• Focus on the core domain
• Explore models in a creative collaboration of domain practitioners and software practitioners
• Speak a ubiquitous language within an explicitly bounded context
http://domainlanguage.com/ddd/patterns/DDD_Reference_2011-01-31.pdf
Problem and chosen solution
Model
UmlAsASketch
UbiquitousLanguage Code
Model, code, etc... How do they fit together?
UI
Demo
Ubiquitous language and bounded context
Argh! Why not come up
with ten more words
for describing the same thing…
Why on Earth does
he care about that?
It’s just words…
Ubiquitous language with Behavior-Driven Development (BDD)As an insurance brokerI want to know who my gold customers areSo that I sell more
Given customer Sven Svensson existsWhen he buys insurance XYZ for 10000 USDThen he becomes a gold customer
Demo
Learning and collaborating
Sigh, he’s coming with that now!?
Sigh, he’s coming with that now!?
A comparison between domain-driven design and database-driven design, a few simple examples
”Customers have rentals”Customer Rental
Some typical T-SQL...IF (SELECT COUNT(*) FROM RentalLines
INNER JOIN Products ON RentalLines.ProductId = Products.Id WHERE RentalId = inserted.Id AND RequiredAge > @ageOfCustomer) > 0 BEGIN
ROLLBACK RAISERROR... RETURN
END
UPDATE Rentals SET Status = 4 WHERE Id = inserted.IdAND Status = 3SELECT @anError = @@ERROR, @aRowCount = @@ROWCOUNT
...
Another approach, first try...public bool CanCheckOut(){ if (status != RentalStatus.New) return false;
if (Customer.Age < highestRequiredAgeOfAnyOfTheChosenFilms())
return false;
return true;} public void CheckOut(){ if (! CanCheckOut()) throw new...
...
status = RentalStatus.CheckedOut;}
Transaction Script vs Domain Model
vs
If I can only talk about one tactical pattern…
Value Objects
Like this?var stinasEggs = 7 * 12;
var pellesEggs = 3 * 20;
var theNumberOfEggsInTheBasket = stinasEggs + pellesEggs;
Assert.AreEqual(144, theNumberOfEggsInTheBasket);
Or like this?var stinasEggs = Amount.Dozen(7);
var pellesEggs = Amount.Score(3);
var theNumberOfEggsInTheBasket = stinasEggs + pellesEggs;
Assert.AreEqual(144, theNumberOfEggsInTheBasket.Count);
Architectural styles for implementing DDD
Classic layering (n-tier)
UI Facade EntitiesData
AccessTables
Most often very little focus
Traveling recordsets...
Starting point now for layering
UI Domain Model
Relaxed focus on layering, more focus on……bounded contexts!
With application databases instead of integration databasesAnd balancing loose coupling and high cohesion
Maybe you now believe you can benefit from DDD... Now what?
What follows is definitely not a prescriptive guidance...
…just an example!
Demo
“Process”
Time report…
“Process” or more like a typical flowA little strategic design
A story and scenarioUI sketchingSome UmlAsASketchTransform the scenario into an acceptance test
Test drive the needed pieces
Next story, and so on...
SummaryChallenge
Domain-Driven Design
Related contentAll the presentations at this track:Cesar de la Torre: Positioning Microsoft Development Technologies for Custom Application Development (DEV-B204)Per Rovegård: Real Experience and Architectural DDD Patterns Applied on .NET (DEV-B343)Julie Lerman: Entity Framework in Core Business Applications and DDD Approaches (DEV-B336)Greg Young: .NET Event Driven Applications, CQRS and Event Sourcing in Mission-Critical Applications (DEV-B401)Miguel Castro: Understanding Dependency Injection and Those Pesky Containers (DEV-B207)BooksEric Evans: Domain-Driven DesignJimmy Nilsson: Applying Domain-Driven Design and PatternsVaughn Vernon: Implementing Domain-Driven Design
Find Me Later At this trackor at jimmy.nilsson@factor10.com
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© 2013 Microsoft Corporation. All rights reserved. Microsoft, Windows and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.
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