m09-domain

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Original

English

🇨🇳

Translation

Chinese

Domain Modeling

领域建模

Layer 2: Design Choices

第2层：设计选择

Core Question

核心问题

What is this concept's role in the domain?

Before modeling in code, understand:

Is it an Entity (identity matters) or Value Object (interchangeable)?
What invariants must be maintained?
Where are the aggregate boundaries?

该概念在领域中的角色是什么？

在进行代码建模前，需明确：

它是Entity（标识至关重要）还是Value Object（可互换）？
必须维护哪些不变量？
聚合边界在哪里？

Domain Concept → Rust Pattern

领域概念 → Rust模式

Domain Concept	Rust Pattern	Ownership Implication
Entity	struct + Id	Owned, unique identity
Value Object	struct + Clone/Copy	Shareable, immutable
Aggregate Root	struct owns children	Clear ownership tree
Repository	trait	Abstracts persistence
Domain Event	enum	Captures state changes
Service	impl block / free fn	Stateless operations

领域概念	Rust模式	所有权说明
Entity	struct + Id	自有、唯一标识
Value Object	struct + Clone/Copy	可共享、不可变
Aggregate Root	struct owns children	清晰的所有权树
Repository	trait	抽象持久化
Domain Event	enum	捕获状态变更
Service	impl block / free fn	无状态操作

Thinking Prompt

思考提示

Before creating a domain type:

What's the concept's identity?
- Needs unique identity → Entity (Id field)
- Interchangeable by value → Value Object (Clone/Copy)
What invariants must hold?
- Always valid → private fields + validated constructor
- Transition rules → type state pattern
Who owns this data?
- Single owner (parent) → owned field
- Shared reference → Arc/Rc
- Weak reference → Weak

在创建领域类型前：

该概念的标识是什么？
- 需要唯一标识 → Entity（含Id字段）
- 可按值互换 → Value Object（实现Clone/Copy）
必须保持哪些不变量？
- 始终有效 → 私有字段 + 已验证的构造函数
- 转换规则 → 类型状态模式
谁拥有该数据？
- 单一所有者（父级） → 自有字段
- 共享引用 → Arc/Rc
- 弱引用 → Weak

Trace Up ↑

向上追溯 ↑

To domain constraints (Layer 3):

"How should I model a Transaction?"
    ↑ Ask: What domain rules govern transactions?
    ↑ Check: domain-fintech (audit, precision requirements)
    ↑ Check: Business stakeholders (what invariants?)

Design Question	Trace To	Ask
Entity vs Value Object	domain-*	What makes two instances "the same"?
Aggregate boundaries	domain-*	What must be consistent together?
Validation rules	domain-*	What business rules apply?

到领域约束（第3层）：

"我应该如何建模Transaction？"
    ↑ 提问：哪些领域规则管控交易？
    ↑ 检查：domain-fintech（审计、精度要求）
    ↑ 检查：业务相关人员（有哪些不变量？）

设计问题	追溯至	提问
Entity vs Value Object	domain-*	什么让两个实例“相同”？
聚合边界	domain-*	哪些内容必须保持一致？
验证规则	domain-*	适用哪些业务规则？

Trace Down ↓

向下追溯 ↓

To implementation (Layer 1):

"Model as Entity"
    ↓ m01-ownership: Owned, unique
    ↓ m05-type-driven: Newtype for Id

"Model as Value Object"
    ↓ m01-ownership: Clone/Copy OK
    ↓ m05-type-driven: Validate at construction

"Model as Aggregate"
    ↓ m01-ownership: Parent owns children
    ↓ m02-resource: Consider Rc for shared within aggregate

到实现（第1层）：

"建模为Entity"
    ↓ m01-ownership: 自有、唯一
    ↓ m05-type-driven: 为Id使用Newtype

"建模为Value Object"
    ↓ m01-ownership: 可实现Clone/Copy
    ↓ m05-type-driven: 在构造时验证

"建模为Aggregate"
    ↓ m01-ownership: 父级拥有子级
    ↓ m02-resource: 考虑在聚合内使用Rc实现共享

Quick Reference

快速参考

DDD Concept	Rust Pattern	Example
Value Object	Newtype	`struct Email(String);`
Entity	Struct + ID	`struct User { id: UserId, ... }`
Aggregate	Module boundary	`mod order { ... }`
Repository	Trait	`trait UserRepo { fn find(...) }`
Domain Event	Enum	`enum OrderEvent { Created, ... }`

DDD概念	Rust模式	示例
Value Object	Newtype	`struct Email(String);`
Entity	Struct + ID	`struct User { id: UserId, ... }`
Aggregate	模块边界	`mod order { ... }`
Repository	Trait	`trait UserRepo { fn find(...) }`
Domain Event	Enum	`enum OrderEvent { Created, ... }`

Pattern Templates

模式模板

Value Object

rust

struct Email(String);

impl Email {
    pub fn new(s: &str) -> Result<Self, ValidationError> {
        validate_email(s)?;
        Ok(Self(s.to_string()))
    }
}

rust

struct Email(String);

impl Email {
    pub fn new(s: &str) -> Result<Self, ValidationError> {
        validate_email(s)?;
        Ok(Self(s.to_string()))
    }
}

Entity

rust

struct UserId(Uuid);

struct User {
    id: UserId,
    email: Email,
    // ... other fields
}

impl PartialEq for User {
    fn eq(&self, other: &Self) -> bool {
        self.id == other.id  // Identity equality
    }
}

rust

struct UserId(Uuid);

struct User {
    id: UserId,
    email: Email,
    // ... 其他字段
}

impl PartialEq for User {
    fn eq(&self, other: &Self) -> bool {
        self.id == other.id  // 标识相等性
    }
}

Aggregate

rust

mod order {
    pub struct Order {
        id: OrderId,
        items: Vec<OrderItem>,  // Owned children
        // ...
    }

    impl Order {
        pub fn add_item(&mut self, item: OrderItem) {
            // Enforce aggregate invariants
        }
    }
}

rust

mod order {
    pub struct Order {
        id: OrderId,
        items: Vec<OrderItem>,  // 自有子级
        // ...
    }

    impl Order {
        pub fn add_item(&mut self, item: OrderItem) {
            // 强制执行聚合不变量
        }
    }
}

Common Mistakes

常见错误

Mistake	Why Wrong	Better
Primitive obsession	No type safety	Newtype wrappers
Public fields with invariants	Invariants violated	Private + accessor
Leaked aggregate internals	Broken encapsulation	Methods on root
String for semantic types	No validation	Validated newtype

错误	原因	优化方案
原始类型滥用	无类型安全性	使用Newtype包装器
带不变量的公共字段	不变量可能被破坏	私有字段 + 访问器
暴露聚合内部细节	破坏封装性	在根实体上实现方法
用字符串表示语义类型	无验证	已验证的Newtype

When	See
Type-driven implementation	m05-type-driven
Ownership for aggregates	m01-ownership
Domain error handling	m13-domain-error
Specific domain rules	domain-*

场景	参考
类型驱动实现	m05-type-driven
聚合的所有权	m01-ownership
领域错误处理	m13-domain-error
特定领域规则	domain-*

m09-domain

Original

Translation

Domain Modeling

领域建模

Core Question

核心问题

Domain Concept → Rust Pattern

领域概念 → Rust模式

Thinking Prompt

思考提示

Trace Up ↑

向上追溯 ↑

Trace Down ↓

向下追溯 ↓

Quick Reference

快速参考

Pattern Templates

模式模板

Value Object

Value Object

Entity

Entity

Aggregate

Aggregate

Common Mistakes

常见错误

Related Skills

相关技能