ビジネスエンティティの設計
企業全体にわたるビジネスルールをカプセル化し、安定性を保つ中核のビジネスオブジェクト（Entities）を定義します。
「ビジネスエンティティの設計」はCoddyKit上の無料Clean Architecture & Design Patterns in Practiceレッスンです。 これはレッスン1/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはClean Architecture & Design Patterns in Practice学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Clean Architecture & Design Patterns in Practiceコースには全4レッスンが含まれています。
このレッスンの一部はまだ翻訳されておらず、英語で表示されています。
What are Business Entities?
In Clean Architecture, Entities are the heart of your application. They represent the core business concepts and rules that are crucial to your enterprise.
Think of them as the fundamental building blocks that define "what your business is" and "how it works," independent of how you store or display data.
Core Business Rules
Entities encapsulate enterprise-wide business rules. These are rules that would exist even if there were no software system, like "a product must have a positive price" or "an order must have a customer."
These rules are stable and apply across your entire organization, not just a specific part of your application.
Independent & Stable
A key principle of Entities is their independence. They should not depend on external layers like databases, web frameworks, or UI components.
This makes them the most stable part of your application, changing only when the core business rules themselves change, not when technology does.
Entity vs. DTO
It's important to distinguish an Entity from a simple Data Transfer Object (DTO). A DTO is just a bag of data, often used to move data between layers.
An Entity, however, contains both data and behavior. It actively enforces its own business rules through its methods.
Entity Structure
Typically, an Entity includes:
- Attributes: The data that describes the business object (e.g., name, ID, price).
- Methods: The operations that can be performed on the entity, enforcing its business rules and maintaining its integrity.
These methods ensure the entity always remains in a valid state according to your business logic.
Example: `Product` Entity
Let's consider a simple Product entity. What data and rules would it need?
- A product needs an
id,name, andprice. - A core business rule might be: "A product's price must always be positive."
The entity itself should enforce this rule.
`Product` Entity Code
Here's how a basic Product entity might look in Java, ensuring the price rule:
public class Product {
private String id;
private String name;
private double price;
public Product(String id, String name, double price) {
if (price <= 0) {
throw new IllegalArgumentException("Price must be positive.");
}
this.id = id;
this.name = name;
this.price = price;
}
public String getId() { return id; }
public String getName() { return name; }
public double getPrice() { return price; }
public static void main(String[] args) {
try {
Product laptop = new Product("P001", "Laptop", 1200.00);
System.out.println(laptop.getName() + " costs $" + laptop.getPrice());
// This would throw an error:
// Product invalid = new Product("P002", "Free Item", 0.00);
} catch (IllegalArgumentException e) {
System.out.println("Error creating product: " + e.getMessage());
}
}
}Entity Behavior & Rules
Entities aren't just data containers; they have methods that encapsulate behavior and enforce rules. For example, applying a discount might have its own business logic.
The entity's methods ensure its internal state remains consistent and valid according to business rules.
`Product` Discount Example
Let's add a method to our Product entity to apply a discount, with a rule that discounts can't make the price negative.
public class Product {
private String id;
private String name;
private double price;
public Product(String id, String name, double price) {
if (price <= 0) {
throw new IllegalArgumentException("Price must be positive.");
}
this.id = id;
this.name = name;
this.price = price;
}
public String getId() { return id; }
public String getName() { return name; }
public double getPrice() { return price; }
// New method to apply discount
public void applyDiscount(double percentage) {
if (percentage < 0 || percentage > 100) {
throw new IllegalArgumentException("Discount must be between 0-100%.");
}
double newPrice = this.price * (1 - percentage / 100);
if (newPrice < 0) { // Ensure price doesn't go negative
this.price = 0;
} else {
this.price = newPrice;
}
}
public static void main(String[] args) {
Product book = new Product("B001", "Clean Code Book", 40.00);
System.out.println("Original: " + book.getName() + " $" + book.getPrice());
book.applyDiscount(25); // 25% discount
System.out.println("Discounted: " + book.getName() + " $" + book.getPrice());
try {
book.applyDiscount(150); // Invalid discount
} catch (IllegalArgumentException e) {
System.out.println("Error applying discount: " + e.getMessage());
}
}
}Entity Properties Check
Based on what we've learned, which of the following are true characteristics of a Clean Architecture Entity?
Recap: Designing Entities
Great job! You've learned about Entities in Clean Architecture. Key takeaways:
- Entities represent your core business concepts.
- They encapsulate enterprise-wide business rules.
- Entities contain both data and behavior, actively enforcing their rules.
- They are independent and stable, not tied to frameworks or external layers.
Next, we'll explore how Use Cases interact with these robust entities to perform application-specific tasks.
よくある質問
「ビジネスエンティティの設計」レッスンは無料ですか？
はい。「ビジネスエンティティの設計」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Clean Architecture & Design Patterns in Practiceコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Clean Architecture & Design Patterns in Practiceコースには全4レッスンが含まれています。
「ビジネスエンティティの設計」で何を学びますか？
企業全体にわたるビジネスルールをカプセル化し、安定性を保つ中核のビジネスオブジェクト（Entities）を定義します。 ブラウザで直接実行するハンズオンコードでClean Architecture & Design Patterns in Practiceを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。
Clean Architecture & Design Patterns in Practiceを始めるのに経験は必要ですか？
事前経験は必要ありません。CoddyKitのClean Architecture & Design Patterns in Practiceは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン1/4です。
「ビジネスエンティティの設計」レッスンにはどのくらい時間がかかりますか？
ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。
このClean Architecture & Design Patterns in Practiceレッスンでコードを書いて実行できますか？
はい。すべてのClean Architecture & Design Patterns in Practiceレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。