1. http://www.umlchina.com Building an Offline Smart Client using Domain-Driven Design Principles Tim McCarthy

2. Agenda 1.DDD Definitions/Patterns 2.The SmartCA Application 3.Designing the Layered Architecture 4.WPF and the Model-View-ViewModel Pattern 5.Synchronizing the Data

3. Agenda 1.DDD Definitions/Patterns 2.The SmartCA Application 3.Designing the Layered Architecture 4.WPF and the Model-View-ViewModel Pattern 5.Synchronizing the Data

4. What is Domain-Driven Design (DDD)? Sponsor Logo

5. Why Domain-Driven Design (DDD)?  Most development time is still spent writing plumbing code instead of business logic  Typically, the UI will change a LOT more than the business logic  The model is a great tool for communication between developers and users .NET has good support for it!

6. Ubiquitous Language  Common terms between business experts and development team  Use the language in your code  Namespaces  Class, property, method, variable names

7. Communicating the Language  Create whiteboard drawings  Favor whiteboarding over Visio  Use digital camera to capture, then paste into Word  Use Visual Studio class diagrams for core parts of the domain  Code and diagram are kept in sync  No wasted time diagramming, your diagram is the code

8. Definition: Entities  An object defined primarily by its identity  Not its attributes  Could be a person, a customer, an order, etc.  Not all objects have meaningful identities…  In some systems, a class may be an ENTITY, in others maybe not

9. Definition: Value Objects  Represent an aspect of the domain with NO conceptual identity  Use when you care about what something is, not who they are  Same thing as a DTO [Fowler PoEAA]  Simple, immutable objects

10. Definition: Aggregates  A cluster of associated objects treated as a unit for the purpose of data changes  They have a root and a boundary  Boundary = what is inside the AGGREGATE  Root = single ENTITY inside the AGGREGATE  Hardest but most important concept to understand in DDD!

11. Aggregate Rules  The root ENTITY has global identity  ENTITIES inside the boundary have local identity  Nothing outside the AGGREGATE boundary can hold a reference to anything inside, except to the root ENTITY  Objects in the AGGREGATE can hold references to other AGGREGATE roots  …a few more

12. Definition: Services  An operation offered as an interface that stands alone in the model  Does not fit into any of the objects in the model  Stateless  To be used judiciously (do not turn your app into a Transaction Script)  Use when an operation is an important domain concept

13. Pattern: Layered Supertype [Fowler 475]  Type that acts as the supertype for all types in its layer, i.e. a base class!  Factors out common features, such as handling the identity of ENTITIES  Example: a common Id property  Helps eliminate duplicate code

14. Pattern: Repository  Provide access to AGGREGATE roots  Represents all objects of a certain type as a conceptual set (usually emulated)  Behaves like a collection, e.g. Add(), Remove(), FindBy(id), etc.  Persistence Ignorance!

15. Pattern: Layered Architecture

16. Agenda 1.DDD Definitions/Patterns 2.The SmartCA Application 3.Designing the Layered Architecture 4.WPF and the Model-View-ViewModel Pattern 5.Synchronizing the Data

17. The SmartCA Application  Problem – Legacy MS Access Application  a.k.a. Smart Client Anti-Pattern  New System Requirements  Technologies  Layered Architecture

18. The Legacy Application

19. New System Requirements  Reliability and Availability  Scalability  Maintainability  Rich client application functionality  Offline Capable  Intelligent installation and auto-update functionality  Additional client device support

20. The New Solution – SmartCA Application  DDD with Layered Architecture  UI = WPF Smart Client  Data Store  Server – behind web services cloud  Client – SQL Server Compact Edition 3.5

21. Agenda 1.DDD Definitions/Patterns 2.The SmartCA Application 3.Designing the Layered Architecture 4.WPF and the Model-View-ViewModel Pattern 5.Synchronizing the Data

22. The Layered Architecture  Application Layer  Domain Layer  Repository Strategy  Layered Supertype Pattern  Infrastructure Layer  Presentation Layer

23. Demonstration #1  Layers represented in the SmartCA Visual Studio Solution

24. Repository Framework  Interfaces  Repository Factory  Unit of Work  Repository Base Classes

25. Demonstration #2  Repository Framework Implementation

26. Mapping - Entity Factory Framework  Interfaces  Entity Factory Builder

27. Demonstration #3  Entity Factory Framework Implementation

28. Agenda 1.DDD Definitions/Patterns 2.The SmartCA Application 3.Designing the Layered Architecture 4.WPF and the Model-View-ViewModel Pattern 5.Synchronizing the Data

29. Windows Presentation Foundation (WPF)  Declarative Programming (Using XAML)  Built-in Command Pattern  Strong Data Binding Support

30. Model-View-ViewModel Pattern  Traditional Presentation Patterns  MVP  MVC  More…  Model-View-ViewModel Definition  What’s a ViewModel?

31. Demonstration #4  Model-View-ViewModel

32. Agenda 1.DDD Definitions/Patterns 2.The SmartCA Application 3.Designing the Layered Architecture 4.WPF and the Model-View-ViewModel Pattern 5.Synchronizing the Data

33. Synchronizing the Data – Some Choices  SQL Replication  ADO.NET Synchronization Services  Message-Based  Taking advantage of Unit of Work  Can talk to any message-based server

34. Message-Base Synchronization

35. Demonstration #5  Data Synchronization

36. Resources  [Evans]: Domain-Driven Design: Tackling Complexity in the Heart of Software, Evans, Addison-Wesley (2003)  [Fowler]: Patterns of Enterprise Application Architecture, Fowler, Addison- Wesley (2003)  [Nilsson]: Applying Domain Driven Design and Patterns: using.NET, Addison Wesley 2006

37. Tim McCarthy, InterKnowlogy  Get the Demos & PPT at:  Slides: http://www.umlchina.com  Code: codeplex.com/dddpdscodeplex.com/dddpds .NET Domain-Driven Design with C#: Problem- Design-Solution.NET Domain-Driven Design with C#: Problem- Design-Solution  Contact me: Tim McCarthy  E-mail : tmccart1@san.rr.comtmccart1@san.rr.com  About Tim McCarthy .NET Architect/Dev Lead/Trainer  Author / Speaker  MCSD, MCSD.NET, MCDBA, MCT,  IEEE CSDP