Apex Service Layer Design

🧱 Apex Service Layer Design: Helper & Handler Classes

In Apex, the **Service Layer pattern** is used to organize logic in a modular and scalable way. It separates your **trigger logic**, **business logic**, and **utility logic** into focused components:

• Trigger → Handler Class: Controls the flow based on the context.
• Handler → Helper Class: Performs the actual business logic.

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📐 Why Use Service Layer?

• 🔄 Makes code reusable and easier to test
• 🧪 Simplifies unit testing by separating concerns
• ⚙️ Prevents logic inside triggers directly (recommended best practice)

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📁 Folder Structure (Conceptual)

/triggers
  AccountTrigger.trigger

/classes
  AccountTriggerHandler.cls
  AccountHelper.cls

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1️⃣ Trigger File

This is just a delegator, calling the handler class.

AccountTrigger.trigger

trigger AccountTrigger on Account (before insert, after update) {
    AccountTriggerHandler.handle(Trigger.isBefore, Trigger.isAfter);
}
  

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2️⃣ Trigger Handler Class

This class controls which logic to call based on the trigger context.

AccountTriggerHandler.cls

public class AccountTriggerHandler {
    public static void handle(Boolean isBefore, Boolean isAfter) {
        if (isBefore && Trigger.isInsert) {
            AccountHelper.setDefaultRating(Trigger.new);
        }
        if (isAfter && Trigger.isUpdate) {
            AccountHelper.logChanges(Trigger.oldMap, Trigger.newMap);
        }
    }
}
  

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3️⃣ Helper Class

Contains the actual logic. You can reuse these methods anywhere.

AccountHelper.cls

public class AccountHelper {

    public static void setDefaultRating(List accList) {
        for (Account acc : accList) {
            if (String.isBlank(acc.Rating)) {
                acc.Rating = 'Hot';
            }
        }
    }

    public static void logChanges(Map oldMap, Map newMap) {
        for (Id accId : newMap.keySet()) {
            Account oldAcc = oldMap.get(accId);
            Account newAcc = newMap.get(accId);
            if (oldAcc.Name != newAcc.Name) {
                System.debug('Account Name changed from ' + oldAcc.Name + ' to ' + newAcc.Name);
            }
        }
    }
}
  

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📊 Handler vs Helper

Component	Responsibility	Example Method
Trigger Handler	Controls logic flow (like a traffic cop)	handle(Boolean isBefore, Boolean isAfter)
Helper Class	Contains business logic methods	setDefaultRating(), logChanges()

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✅ Best Practices

• Keep triggers logic-free
• Write unit tests for helper methods directly
• Follow naming conventions like ObjectNameTriggerHandler
• Make helper methods public static for reuse