Domain-Driven DesignDomain-Driven Designusing the ADO.NET Entity using the ADO.NET Entity FrameworkFramework
Tim McCarthyTim McCarthyPrincipal Engineer, Principal Engineer, [email protected]@interknowlogy.com
About…About…InterKnowlogy InterKnowlogy ((www.InterKnowlogy.com))
Tim McCarthy, Principal EngineerTim McCarthy, Principal EngineerCustom App Dev / Consulting / Software Custom App Dev / Consulting / Software Engineering Firm headquartered in Carlsbad, CAEngineering Firm headquartered in Carlsbad, CAMicrosoft Gold Partner managed in SoCal and Microsoft Gold Partner managed in SoCal and RedmondRedmondDesign, Architect, Build and Deploy enterprise Design, Architect, Build and Deploy enterprise class applications class applications Industry Experts:Industry Experts:
90% of the company is published90% of the company is publishedMicrosoftMicrosoft®® .NET Application development for 5+ years! .NET Application development for 5+ years!MicrosoftMicrosoft® ® .NET Smart Client pioneers / industry leaders.NET Smart Client pioneers / industry leadersInformation Worker SolutionsInformation Worker SolutionsIntegration / Messaging, B2B / B2C, Wireless / Mobility Integration / Messaging, B2B / B2C, Wireless / Mobility MicrosoftMicrosoft®® SharePoint, Microsoft SharePoint, Microsoft®® BizTalk BizTalk®® Web Services, Web Services, MicrosoftMicrosoft®® Active Directory Active Directory®®, Security, SSO, Authorization, , Security, SSO, Authorization, AuthenticationAuthenticationSolutions on the emerging Microsoft serversSolutions on the emerging Microsoft serversLargest Client: MicrosoftLargest Client: Microsoft
AgendaAgenda
Organizing Domain LogicOrganizing Domain Logic
What is DDD?What is DDD?
Why Domain-Driven Design (DDD)?Why Domain-Driven Design (DDD)?
DDD Definitions/PatternsDDD Definitions/Patterns
ADO.NET Entity FrameworkADO.NET Entity Framework
When is DDD appropriate?When is DDD appropriate?
Organizing Domain LogicOrganizing Domain Logic
Transaction ScriptTransaction Script
Domain ModelDomain Model
Table ModuleTable Module
Choosing the Right Choosing the Right ApproachApproach
Demo: Organizing Demo: Organizing Domain LogicDomain Logic
What is DDD?What is DDD?
encapsulate with
MODEL-DRIVEN
DESIGN
express model with
isolate domain with
encapsulate with
ENTITIES
VALUE OBJECTS
LAYERED
ARCHITECTURE
AGGREGATES
REPOSITORIES
act as root of
SMART UI
X
FACTORIES
encapsulate with
express model with
encapsulate with
mutually exclusivechoices
access with
maintain integrity with
access withSERVICES
express model with
Why Domain-Driven Why Domain-Driven Design (DDD)?Design (DDD)?
Most development time is still spent Most development time is still spent writing plumbing code instead of writing plumbing code instead of business logicbusiness logic
Typically, the UI will change a LOT Typically, the UI will change a LOT more than the business logicmore than the business logic
The model is a great tool for The model is a great tool for communication between developers communication between developers and usersand users
.NET has good support for it!.NET has good support for it!
Ubiquitous LanguageUbiquitous Language
Common terms between business Common terms between business experts and development teamexperts and development team
Use the language in your codeUse the language in your codeNamespacesNamespaces
Class, property, method, variable namesClass, property, method, variable names
Communicating the Communicating the LanguageLanguage
Create whiteboard drawingsCreate whiteboard drawingsFavor whiteboarding over VisioFavor whiteboarding over Visio
Use digital camera to capture, then Use digital camera to capture, then paste into Wordpaste into Word
Use Visual Studio class diagrams for Use Visual Studio class diagrams for core parts of the domaincore parts of the domain
Code and diagram are kept in syncCode and diagram are kept in sync
No wasted time diagramming, your No wasted time diagramming, your diagram is the codediagram is the code
Definition: EntitiesDefinition: Entities
An object defined primarily by its An object defined primarily by its identityidentity
Not its attributesNot its attributes
Could be a person, a customer, an Could be a person, a customer, an order, etc.order, etc.
Not all objects have meaningful Not all objects have meaningful identities…identities…
In some systems, a class may be an In some systems, a class may be an ENTITY, in others maybe notENTITY, in others maybe not
Definition: Value ObjectsDefinition: Value Objects
Represent an aspect of the domain Represent an aspect of the domain with NO conceptual identitywith NO conceptual identity
Use when you care about Use when you care about whatwhat something is, not something is, not whowho they are they are
Same thing as a DTO [Fowler PoEAA]Same thing as a DTO [Fowler PoEAA]
Simple, immutable objectsSimple, immutable objects
Definition: AggregatesDefinition: Aggregates
A cluster of associated objects A cluster of associated objects treated as a unit for the purpose of treated as a unit for the purpose of data changesdata changes
They have a root and a boundaryThey have a root and a boundaryBoundary = what is inside the Boundary = what is inside the AGGREGATEAGGREGATE
Root = single ENTITY inside the Root = single ENTITY inside the AGGREGATEAGGREGATE
Most important concept to Most important concept to understand in modelling!understand in modelling!
Aggregate RulesAggregate Rules
The root ENTITY has global identityThe root ENTITY has global identity
ENTITIES inside the boundary have ENTITIES inside the boundary have local identitylocal identity
Nothing outside the AGGREGATE Nothing outside the AGGREGATE boundary can hold a reference to boundary can hold a reference to anything inside, except to the root anything inside, except to the root ENTITY ENTITY
Objects in the AGGREGATE can hold Objects in the AGGREGATE can hold references to other AGGREGATE references to other AGGREGATE rootsroots
……a few morea few more
Definition: ServicesDefinition: Services
An operation offered as an interface An operation offered as an interface that stands alone in the modelthat stands alone in the model
Does not fit into any of the objects in Does not fit into any of the objects in the modelthe model
StatelessStateless
To be used judiciously (do not turn To be used judiciously (do not turn your app into a Transaction Script)your app into a Transaction Script)
Use when an operation is an Use when an operation is an important domain conceptimportant domain concept
Pattern: Layered Pattern: Layered Supertype Supertype [Fowler 475][Fowler 475]
Type that acts as the supertype for Type that acts as the supertype for all types in its layer, i.e. a base class!all types in its layer, i.e. a base class!
Factors out common features, such Factors out common features, such as handling the identity of ENTITIESas handling the identity of ENTITIES
Example: a common Id propertyExample: a common Id property
Helps eliminate duplicate codeHelps eliminate duplicate code
Pattern: RepositoryPattern: Repository
Provide access to AGGREGATE rootsProvide access to AGGREGATE roots
Represents all objects of a certain Represents all objects of a certain type as a conceptual set (usually type as a conceptual set (usually emulated)emulated)
Behaves like a collection, e.g. Add(), Behaves like a collection, e.g. Add(), Remove(), FindBy(id), etc.Remove(), FindBy(id), etc.
Persistence Ignorance!Persistence Ignorance!
Pattern: Layered Pattern: Layered ArchitectureArchitecture
Infrastructure Persistence Infrastructure Persistence StrategiesStrategies
Remember, Domain Model is Remember, Domain Model is Persistent Ignorant!Persistent Ignorant!
ApproachesApproachesCustom Manual CodeCustom Manual Code
Code GenerationCode Generation
Metadata Mapping (O/R Mapping)Metadata Mapping (O/R Mapping)
ADO.NET Entity ADO.NET Entity Framework: GoalsFramework: Goals
Raise abstraction Raise abstraction Level for Data Level for Data Programming Programming
Get Rid of the Get Rid of the PlumbingPlumbing
ADO.NET Entity ADO.NET Entity FrameworkFramework
ProvidesProvidesMapping from relational data to .NET Mapping from relational data to .NET classesclasses
Auto-generation of both mapping and Auto-generation of both mapping and entitiesentities
Uses a New Data ProviderUses a New Data ProviderThe EntityClient ProviderThe EntityClient Provider
SupportsSupportsQuerying over entitiesQuerying over entities
Relationship navigationRelationship navigation
Entity InheritanceEntity Inheritance
ADO.NET Entity ADO.NET Entity Framework: Metadata Framework: Metadata StructureStructure
Demo: Entity FrameworkDemo: Entity Framework
Entity Framework: Entity Framework: ImpressionsImpressions
Great Great HopeHope for the future, but for the future, but PainPain for the presentfor the present
EDM designer not there yet (after EDM designer not there yet (after Orcas)Orcas)
Does not currently support Does not currently support Persistence Ignorance, but the team Persistence Ignorance, but the team is working on itis working on it
Rich change-tracking supportRich change-tracking support
DDD Revisited…DDD Revisited…
encapsulate with
MODEL-DRIVEN
DESIGN
express model with
isolate domain with
encapsulate with
ENTITIES
VALUE OBJECTS
LAYERED
ARCHITECTURE
AGGREGATES
REPOSITORIES
act as root of
SMART UI
X
FACTORIES
encapsulate with
express model with
encapsulate with
mutually exclusivechoices
access with
maintain integrity with
access withSERVICES
express model with
When is DDD AppropriateWhen is DDD Appropriate
“If an unsophisticated team with a simple project decides to try a model-driven design with layered architecture, it will face a difficult learning curve. ... The overhead of managing infrastructure and layers makes very simple tasks take longer. Simple projects come with short time lines and modest expectations.”
Domain-Driven Design by Eric Evans, p76
ResourcesResources
[Evans]: Domain-Driven Design: [Evans]: Domain-Driven Design: Tackling Complexity in the Heart of Tackling Complexity in the Heart of Software, Evans, Addison-Wesley Software, Evans, Addison-Wesley (2003)(2003)
[Fowler]: Patterns of Enterprise [Fowler]: Patterns of Enterprise Application Architecture, Fowler, Application Architecture, Fowler, Addison-Wesley (2003)Addison-Wesley (2003)
[Nilsson]: Applying Domain Driven [Nilsson]: Applying Domain Driven Design and Patterns: using .NETDesign and Patterns: using .NET
Tim McCarthy, Tim McCarthy, InterKnowlogyInterKnowlogy
Get the Demos & PPT at:Get the Demos & PPT at:Blogs.InterKnowlogy.com/TimMcCarthyBlogs.InterKnowlogy.com/TimMcCarthy
More info on InterKnowlogy:More info on InterKnowlogy:www.InterKnowlogy.com
Contact me: Tim McCarthyContact me: Tim McCarthy
E-mailE-mail: : [email protected]@InterKnowlogy.com
Phone:Phone: 760-930-0075 x205 760-930-0075 x205
About Tim McCarthyAbout Tim McCarthy.NET Architect/Dev Lead/Trainer.NET Architect/Dev Lead/TrainerAuthor / SpeakerAuthor / SpeakerMCSD, MCSD.NET, MCDBA, MCT, MCSD, MCSD.NET, MCDBA, MCT, IEEE CSDPIEEE CSDP
