Apex Triggers - 15 (Amazon Interview Question)

 1. Scenario Overview

This automation solves an Amazon Interview Question based on a parent-child relationship between a parent object, Tax_Firm__c, and a child object, Employee__c . The parent features two currency fields: Max_Salary__c and Min_Salary__c . The system must dynamically recalculate and roll up the highest and lowest employee salary values to these parent fields whenever any child employee record is inserted, updated, deleted, or undeleted .

Additionally, the solution handles the edge case where all related employees are deleted from a firm, safely resetting the parent summary values to zero instead of leaving stale metrics behind .

or

Show the Min & Max Salary of Employee records on the Parent Company record.

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2. Apex Handler Class

java

public class EmployeeTriggerHandler {
    public static void updateSalaryRollups(List<Employee__c> newEmployees, Map<Id, Employee__c> oldEmployeeMap) {
        Set<Id> taxFirmIds = new Set<Id>();
        
        // Step 1: Collect impacted Parent Tax Firm IDs across various record lifecycles
        if (newEmployees != null) {
            for (Employee__c emp : newEmployees) {
                if (emp.Tax_Firm__c != null) {
                    taxFirmIds.add(emp.Tax_Firm__c);
                }
                // Handle lookup re-parenting changes: track the previous parent record
                if (oldEmployeeMap != null && oldEmployeeMap.containsKey(emp.Id)) {
                    Employee__c oldEmp = oldEmployeeMap.get(emp.Id);
                    if (oldEmp.Tax_Firm__c != null && oldEmp.Tax_Firm__c != emp.Tax_Firm__c) {
                        taxFirmIds.add(oldEmp.Tax_Firm__c);
                    }
                }
            }
        }
        
        if (taxFirmIds.isEmpty()) {
            return;
        }
        
        // Step 2: Initialize map with default zero-out records for all tracked firms to handle total deletions
        Map<Id, Tax_Firm__c> taxFirmsToUpdateMap = new Map<Id, Tax_Firm__c>();
        for (Id firmId : taxFirmIds) {
            Tax_Firm__c defaultFirm = new Tax_Firm__c();
            defaultFirm.Id = firmId;
            defaultFirm.Max_Salary__c = 0;
            defaultFirm.Min_Salary__c = 0;
            taxFirmsToUpdateMap.put(firmId, defaultFirm);
        }
        
        // Step 3: Run aggregate query to find the actual min and max values for firms that have employees
        List<AggregateResult> groupedResults = [
            SELECT Tax_Firm__c firmId, MAX(Salary__c) maxSal, MIN(Salary__c) minSal 
            FROM Employee__c 
            WHERE Tax_Firm__c IN :taxFirmIds AND Salary__c != null 
            GROUP BY Tax_Firm__c
        ];
        
        // Step 4: Populate calculated values into the update map, overwriting defaults where employees exist
        for (AggregateResult ar : groupedResults) {
            Id firmId = (Id)ar.get('firmId');
            Tax_Firm__c firmRecord = taxFirmsToUpdateMap.get(firmId);
            
            firmRecord.Max_Salary__c = (Decimal)ar.get('maxSal');
            firmRecord.Min_Salary__c = (Decimal)ar.get('minSal');
        }
        
        // Step 5: Perform bulk DML operation outside of loops
        if (!taxFirmsToUpdateMap.isEmpty()) {
            update taxFirmsToUpdateMap.values();
        }
    }
}

Use code with caution.

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3. Apex Trigger

java

trigger EmployeeTrigger on Employee__c (after insert, after update, after delete, after undelete) {
    // Route records to handler processing frameworks inside after-commit lifecycle stages
    if (Trigger.isAfter) {
        if (Trigger.isInsert || Trigger.isUndelete) {
            EmployeeTriggerHandler.updateSalaryRollups(Trigger.new, null);
        } else if (Trigger.isUpdate) {
            EmployeeTriggerHandler.updateSalaryRollups(Trigger.new, Trigger.oldMap);
        } else if (Trigger.isDelete) {
            EmployeeTriggerHandler.updateSalaryRollups(Trigger.old, null);
        }
    }
}