Apex Enterprise Patterns

 Apex Enterprise Patterns are a set of design patterns and best practices for structuring Salesforce applications using Apex. These patterns help create scalable, maintainable, and modular codebases by separating concerns and encapsulating different aspects of your application. Key components include using interfaces, service layers, and domain layers. Here's an overview of how these patterns work, with a focus on interfaces:

1. Domain Layer

• Purpose: Encapsulates the business logic related to a specific Salesforce object (e.g., Account, Opportunity). The Domain Layer operates on the domain model, which represents the data and behavior of the business entities.
• Example:

  
  public class AccountDomain {
      public static void beforeUpdate(List<Account> accounts) {
          for (Account acc : accounts) {
              // Business logic before Account update
          }
      }
  }
  

• Usage: Called from triggers to execute business logic, for example, AccountDomain.beforeUpdate(Trigger.new);.

2. Service Layer

• Purpose: Encapsulates complex business processes and coordinates the interaction between different parts of the system. The service layer is where the application’s business logic resides.
• Example:

  
  public class AccountService {
      public void updateAccounts(List<Account> accounts) {
          // Invoke Domain logic or other services
          AccountDomain.beforeUpdate(accounts);
          update accounts;
      }
  }
  

• Usage: Use the service layer methods in controllers or other services to carry out business processes.

3. Selector Layer

• Purpose: Encapsulates SOQL queries and ensures that querying logic is centralized. It helps in enforcing consistent query practices, such as limiting fields and records returned.
• Example:

  
  public class AccountSelector {
      public static List<Account> selectByStatus(String status) {
          return [SELECT Id, Name FROM Account WHERE Status__c = :status];
      }
  }
  

• Usage: Use selectors to retrieve records rather than writing SOQL directly in other layers, e.g., AccountSelector.selectByStatus('Active');.

4. Unit of Work

• Purpose: Manages the changes to be made to the database and coordinates the final commit of these changes. This pattern helps in keeping track of changes across multiple objects and ensuring they are committed in a controlled manner.
• Example:

  
  public class UnitOfWork {
      private List<SObject> newRecords = new List<SObject>();
      private List<SObject> updatedRecords = new List<SObject>();
  
      public void registerNew(SObject record) {
          newRecords.add(record);
      }
  
      public void registerDirty(SObject record) {
          updatedRecords.add(record);
      }
  
      public void commit() {
          insert newRecords;
          update updatedRecords;
      }
  }
  

• Usage: Track changes using registerNew() or registerDirty(), and commit using commit().

5. Application Layer

• Purpose: Acts as the entry point for all your business logic and service layers. It’s the top layer that orchestrates interactions between different services and processes.
• Example:

  
  public class Application {
      private static final AccountService accountService = new AccountService();
  
      public static AccountService getAccountService() {
          return accountService;
      }
  }
  

• Usage: Access services via the Application layer, e.g., Application.getAccountService().updateAccounts(accounts);.

6. Facade Pattern

• Purpose: Provides a simplified interface to a complex subsystem or set of classes. It hides the complexities and allows for easier interaction with the system.
• Example:

  
  public class AccountFacade {
      public void updateAccountStatus(Id accountId, String status) {
          Account acc = [SELECT Id, Status__c FROM Account WHERE Id = :accountId LIMIT 1];
          acc.Status__c = status;
          update acc;
      }
  }
  

• Usage: Use the facade to carry out complex operations with simple method calls.

7. Interfaces

• Purpose: Interfaces define contracts that classes must adhere to, allowing for loose coupling and flexibility. They are particularly useful in patterns like the Strategy, Factory, and Dependency Injection.
• Example:

  
  public interface IAccountProcessor {
      void process(List<Account> accounts);
  }
  
  public class ActiveAccountProcessor implements IAccountProcessor {
      public void process(List<Account> accounts) {
          // Logic for processing active accounts
      }
  }
  
  public class InactiveAccountProcessor implements IAccountProcessor {
      public void process(List<Account> accounts) {
          // Logic for processing inactive accounts
      }
  }
  

• Usage: Use interfaces to create different implementations that can be swapped out, e.g., IAccountProcessor processor = new ActiveAccountProcessor(); processor.process(accounts);.

8. Trigger Handler Pattern

• Purpose: Separates trigger logic from the trigger itself, improving maintainability and testability. This pattern often leverages the Domain Layer for business logic.
• Example:

  
  public class AccountTriggerHandler extends TriggerHandler {
      public override void beforeUpdate() {
          AccountDomain.beforeUpdate((List<Account>) Trigger.new);
      }
  }
  

• Usage: Associate the handler with the trigger, e.g., trigger AccountTrigger on Account (before update) { new AccountTriggerHandler().run(); }.

9. Dependency Injection

• Purpose: Promotes loose coupling by allowing dependencies to be injected rather than hardcoded within classes. This pattern enhances testability and flexibility.
• Example:

  
  public class AccountController {
      private IAccountProcessor accountProcessor;
  
      public AccountController(IAccountProcessor accountProcessor) {
          this.accountProcessor = accountProcessor;
      }
  
      public void processAccounts(List<Account> accounts) {
          accountProcessor.process(accounts);
      }
  }
  

• Usage: Inject dependencies via constructors or setters, e.g., AccountController controller = new AccountController(new ActiveAccountProcessor()); controller.processAccounts(accounts);.

Summary

Apex Enterprise Patterns promote organized, modular code with clear separation of concerns, making applications easier to maintain, test, and extend. Using interfaces is key to achieving flexibility and loose coupling between components, ensuring that your Salesforce solutions are robust and adaptable to change.