1. How to have your
domain-driven design cake
and eat it, too
Dan Haywood
22 Feb 2010
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2. About me…
 Involved with Naked Objects since 2002
 Committer to the open source framework
 lead developer of a number of sister projects
 Author,"Domain Driven Design using Naked
Objects"
 pragmatic bookshelf
 Senior advisor to the Irish Government
 technical advisor, domain modelling
 coaching on agile development practices
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3. Domain Driven Design
Ubiquitous Language
With a conscious effort by the team, the
domain model can provide the backbone
for that common language
Eric Evans
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4. Roll Call
 Who's read Eric Evans' book,
Domain-Driven design?
 Who's practicising DDD?
 Who's using an ORM?
 Who's using agile methods?
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5. What Is Naked Objects?
 A Principle
 behaviorally complete objects
 An Architectural Pattern
 automatically renders domain objects in an OOUI
 A Framework
 Open source, extensible
 Rapid prototyping & development
 Build webapps or rich client (client/server)
 A bed-fellow for Domain-Driven Design
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6. Naked Objects Pattern
 Business functionality is
encapsulated on the
core business objects
 Objects are exposed
directly & automatically
 All user actions consist of
 creating or retrieving objects,
 forming associations between them
 invoking actions on them
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7. The DRY Principle
 The UI representations
correspond directly
with the underlying
domain object model
 objects and their icons
 object properties / collections
 the menu items available on an object
 eg Claim#submit(Approver)
 desktop icons with repositories / domain services
 eg ClaimRepository, EmployeeRepository
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8. A simple domain model...
0..1
Approver
*
Claim
Claimant Claim
Repository
*
*
Employee Claim
Employee
Repository Item
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9. Naked Objects apps are just pojos
0..1
Approver
*
Claim
Claimant Claim
Repository
*
*
Employee Claim
Employee
Repository Item
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10. But what does a Naked Objects
system look like?
 Let's see...
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11. The Naked Objects
Programming Model
• Dependency injection
Runtime support • Bytecode enhancements
• Declarative business rules
Annotations • Rendering hints
• see it
Business Rules • use it
through Conventions • do it
• know-whats
Behaviorally • know-how-tos
Complete • contributed actions
• Entity
Pojo • Value
• Repository & Services
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12. Naked Objects Framework
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13. Run as webapp or client/server
Web app Client/server
 Context Listener to  Stateless server-side
bootstrap NOF architecture
 ServletFilter to setup  By default, actions
session invoked server-side
 Host HTML viewer,  @ExecutedOn overrides
Scimpi, Restful,  Remoting either via plain
server-side remoting sockets or http
 Transparent lazy loading
of resources
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14. Pluggable Persistence
 In-memory object store
 use composite fixtures
 XML object store
 for casual prototyping
 JPA object store
 uses Hibernate as underlying implementation
 requires @DiscriminatorValue and @Id
 to consistently support @Any associations
 SQL Object Store
 Berkeley DB Object Store
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15. Pluggable Viewers
 DnD Viewer  Eclipse RCP Viewer
 HTML Viewer  in development
 Scimpi Viewer
 Vaadin Viewer
 Headless Viewer  just started
 FitNesse  Others?
 RESTful Viewer  GWT?
 JavaFX?
 NetBeans RCP?
 Flex?
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16. Newer viewers are / will be
customizable
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17. A detail on how to customize
Claim/object-short.shtml
using the Scimpi viewer
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18. Agile acceptance testing
using FitNesse
 Write scenario tests, without writing
fixtures
 Act in same way as Naked Objects viewers
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19. RESTful Support
 Exposes domain objects and properties
as RESTful resources
Object Property Collection Action
GET current state n/a current n/a
of all contents
properties
PUT create set add item n/a
DELETE destroy clear remove item n/a
POST n/a n/a n/a invoke
 Rendered as XHTML using CSS microlanguage
 Write client-side code using JAX-RS annotations
 JBoss RestEasy is underlying implementation`
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20. RESTful XHTML Support
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21. Not an all or nothing affair
 Committing to any new framework is risky
 so don't!
 Just use for prototyping and requirements elicitation
 Minimal dependencies
 Write a conventional front-end (eg Wicket)
 Map to Hibernate or other JPA technology
 Domain model are POJOs after all
 Or, go the whole hog and deploy on Naked Objects
 either rich client or web
 use plugins for Scimpi, Rich Client Objects or DnD
 write your own viewers?
Whichever, Naked Objects is a great way to get into
domain-driven design
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22. Multiple Deployment Options
Embedded Custom Full
Pure Pojo MetaModel Presentation Deployment
• Use as a • Clothe with your • Clothe with • NOF provides all
development own UI your own UI the layers
tool
• NOF provides • NOF handles the • Deploy as a
• Deploy into any the app layer rest webapp
layered
enterprise • Use your own • Deploy as
architecture persistence client/server
layer
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23. Deployment Options
Embedded Metamodel
bootstrap the metamodel
EmbeddedContext context = new MyEmbeddedContext();
NakedObjectsMetaModel nomm = public class Employee … {
new NakedObjectsMetaModel(
context, private String name;
ClaimRepositoryInMemory.class, @MemberOrder(sequence="1")
EmployeeRepositoryInMemory.class); @Disabled
nakedObjectsMetaModel.init(); public String getName() {
return name;
either reach into the metamodel }
public void setName(String lastName) {
NakedObjectSpecification employeeSpec = this.name = lastName;
nomm.getSpecificationLoader() }
.loadSpecification(Employee.class); …
}
NakedObjectAssociation nameAssoc =
employeeSpec.getAssociation("name");
DisabledFacet disabledFacet =
nameAssoc.getFacet(DisabledFacet.class);
System.out.println("Disabled: " + disabledFacet);
or interact using headless viewer
HeadlessViewer viewer = nomm.getViewer();
Employee employee = new Employee();
Employee employeeView =
viewer.view(employee);
employeeView.setName("Joe");
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24. Domain Driven Design
Ubiquitous Language
With a conscious effort by the team, the
domain model can provide the backbone
for that common language
Eric Evans
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25. Domain Driven Design
Ubiquitous Language
Under Naked Objects, there is nothing to
talk about (or with) other than the
domain model ...
so the effort isn't particularly conscious
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26. Before I forget...
 Part 1 – Tools
 DDD core concepts
 Part 2 – Techniques
 Patterns, idioms,
decoupling
 Part 3 – Practices
 FitNesse, Wicket,
JPA/Hibernate, RESTful &
ESBs
www.pragprog.com/titles/dhnako 25% discount code:
zDanHaywoodFeb2010
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27. and don't you forget...
The DDD Exchange
11 June 2010
Please fill in your evaluations
free entrance for one lucky person!
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28. Further Information
Perfection is finally achieved not
when there's no longer anything
to add, but when there's no
longer anything to take away …
when a body has been stripped
down to its nakedness
Antoine de Saint-Exupéry
Contact & Resources
dan@haywood-associates.co.uk
www.danhaywood.com
www.pragprog.com/titles/dhnako
www.nakedobjects.org
starobjects.sourceforge.net
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