1. Brief Introduction to
Domain Driven
Design(DDD)
Yongqiang

2. Outline
 What’s Domain?
 What’s the heart of a software?
 What’s DDD?
 Crunching Knowledge
 Ubiquitous Language
 Basic Elements in DDD
 Summary
 References

3. What’s Domain?
在 DDD 中所指就是企业软件所涉及
 Domain
的业务领域，其中包含大量业务知识。

4. What’s the heart of a software?
 导演-> 软件用户
 剪辑师 -> 软件工程师
剪辑师为什么没有解决导演的
问题？

5.  Theheart of software is its ability to solve
domain-related problems for its users! ( 软
件的核心价值是为客户解决业务问题）。
 如果想做出色的业务软件，前提就是对用
户所处的领域有充分的，全面的，深刻的
理解！

6. What’s DDD?
 领域驱动开发
Evans 创始人
 Eric
 目标：让软件成为领域的映射。
 软件需要具现领域里重要的核心概念和元素，并精
确实现它们之间的关系。
 软件需要对领域进行建模，得到一个关于领域的
模型。
 中心内容：如何将业务领域概念映射到软件工
件中

7. Crunching Knowledge( 知识汲
取)
 Talk with domain expert
 Lead by developers
 Domain model is focused on the most
valuable part
 Developer needs feedback
 We never know enough
 We need knowledge-rich design
 Binding model and implementation

8. Ubiquitous Language( 通用语
言)
 For each term, we need
a very precisely and
unambiguously defined
meaning
 spanning from
discussions with the
domain expert to the
code level
 assures that everybody in
the team shares the
same vision about the
domain and the software.

9. So...
 Modelingout loud!
 One Team, One Language!

10. Basic Elements in DDD

13. Layered Architecture

15. Entity
 An object define primarily by its identity is
called an Entity.
 Most basic responsibility of Entities is to
establish continuity so that behavior can be
clear and predictable. class Person CD
BankAccount
- AccountId
- Deposit
- UserName

16.  Attributes VS. Identity
class Person CD
Person
- BirthDate
- BirthPlace
- Id
- Name
- Parents

17. Value Object( 值对象 )
 An object that represents a descriptive aspect
of the domain with no conceptual identity is
called a VALUE OBJECT.
 VALUE OBJECTS are often passed as
parameters in messages between objects.
class Person CD class Person CD
Point Address
- X: int - City
- Y: int - Street

18.  帮助简化设计
 没有标识符，值
对象可以被轻易
地创建或者丢弃
。
 极力推荐值对象
是不变的。

19. Service( 服务 )
 Some of these are intrinsically activities or
actions, not things.
 A service tends to be named for an activity,
rather that an entity-a verb rather that a
noun.
 A service does not do much on its own; it
would ask other objects to do most of
work.

20.  Partition Services into Layers
 Application
 Domain
 Infrastructure

23. Life Cycle of Domain Object
 Aggregates 聚合
 用于打破对象的网状关系 , 定义所有权和边界
 Factories 工厂
 用于领域对象生命周期的开始部分 , 创建或者重组
复杂的对象或 Aggregates.
 Repositories 资源库
 用于领域对象生命周期的中后部 , 对存储 , 检索查
询等功能进行了封装 .

24. Aggregate( 聚合 )
 An aggregate is a cluster of associated
objects that we treat as a unit for the purpose
of data changes. Each aggregate has a root
of a boundary.
 The root is the only member of the Aggregate
that outside objects are allowed to hold
references.

26.  Invariants,
which are consistency rules that
must be maintained whenever data changes.

27. Factory( 工厂 )
 Creation of an object can be a major
operation in itself, but complex assembly
operations do not fit the responsibility of
the created objects. Combining such
responsibilities can produce ungainly designs
that are hard to understand.
 A program element whose responsibility is
the creation of other objects is called a
FACTORY.

28.  Two basic requirements for any good Factory
are
 Each creation method is atomic and enforces all
invariants of the created object or AGGREGATE.
 The FACTORY should be abstracted to the type
desired, rather than the concrete class(es)
created.

30. Repositories( 资源库 )
 Global Access
 Aggregate roots which are not convenient to
reach by traversal.
 Value Objects with complex internal structure.
 enumerated values.
 Two ways to query a repository
 Hard-coded query with specific parameter.
 Specification-based query.

31. By specific parameter
By criteria

32. Summary
 DDD 目标是建立最适合的模型映射领域知识
，以模型做为团队交流和软件开发的基础。
 DDD 对企业应用软件中的基础元素做了合理
的抽象。
 DDD 可以和 TDD, 敏捷开发方法联合使用。

33. References
 EricEvans 《领域驱动设计—软件核心复杂
性应对之道》
 InfoQ 《领域驱动设计精简版》