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Clean Architecture & Design Patterns in Practice · Aula

Projetando Entidades de Negócio

Defina seus objetos centrais de negócio (Entidades), que encapsulam regras de negócio abrangentes e permanecem estáveis.

Projetando Entidades de Negócio é uma aula grátis de Clean Architecture & Design Patterns in Practice no CoddyKit. Esta é a aula 1 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Clean Architecture & Design Patterns in Practice, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Clean Architecture & Design Patterns in Practice inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

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, and price.
  • 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.

Perguntas Frequentes

A aula “Projetando Entidades de Negócio” é grátis?

Sim — o texto completo de “Projetando Entidades de Negócio” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Clean Architecture & Design Patterns in Practice, atualize para CoddyKit PRO. O curso de Clean Architecture & Design Patterns in Practice inclui 4 aulas no total.

O que vou aprender em “Projetando Entidades de Negócio”?

Defina seus objetos centrais de negócio (Entidades), que encapsulam regras de negócio abrangentes e permanecem estáveis. Você pratica Clean Architecture & Design Patterns in Practice com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar Clean Architecture & Design Patterns in Practice?

Nenhuma experiência prévia é necessária. Clean Architecture & Design Patterns in Practice no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 1 de 4.

Quanto tempo leva a aula “Projetando Entidades de Negócio”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de Clean Architecture & Design Patterns in Practice?

Sim. Cada aula de Clean Architecture & Design Patterns in Practice inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Projetando Entidades de Negócio
  2. Implementando Casos de Uso (Interatores)
  3. Portas de Entrada e Saída
  4. Impondo Regras de Negócio com Invariantes
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