// CORRECT: collect IDs, query once outside the loop
trigger AccountTrigger on Account (before insert, before update) {
    AccountTriggerHandler.handleBeforeInsert(Trigger.new);
}

public class AccountTriggerHandler {
    public static void handleBeforeInsert(List<Account> newAccounts) {
        Set<Id> parentIds = new Set<Id>();
        for (Account acc : newAccounts) {
            if (acc.ParentId != null) parentIds.add(acc.ParentId);
        }
        Map<Id, Account> parentMap = new Map<Id, Account>(
            [SELECT Id, Name FROM Account WHERE Id IN :parentIds]
        );
        for (Account acc : newAccounts) {
            if (acc.ParentId != null && parentMap.containsKey(acc.ParentId)) {
                acc.Description = 'Child of: ' + parentMap.get(acc.ParentId).Name;
            }
        }
    }
}

// INCORRECT: SOQL inside loop — governor limit violation
trigger AccountTrigger on Account (before insert) {
    for (Account acc : Trigger.new) {
        Account parent = [SELECT Id, Name FROM Account WHERE Id = :acc.ParentId]; // BAD
        acc.Description = 'Child of: ' + parent.Name;
    }
}

public class ContactBatchUpdate implements Database.Batchable<SObject> {
    public Database.QueryLocator start(Database.BatchableContext bc) {
        return Database.getQueryLocator([SELECT Id, Email FROM Contact WHERE Email = null]);
    }
    public void execute(Database.BatchableContext bc, List<Contact> scope) {
        for (Contact c : scope) {
            c.Email = 'unknown@example.com';
        }
        Database.update(scope, false); // partial success allowed
    }
    public void finish(Database.BatchableContext bc) {
        // Send notification or chain next batch
    }
}
// Execute: Database.executeBatch(new ContactBatchUpdate(), 200);

@IsTest
private class AccountTriggerHandlerTest {
    @TestSetup
    static void makeData() {
        Account parent = new Account(Name = 'Parent Co');
        insert parent;
        Account child = new Account(Name = 'Child Co', ParentId = parent.Id);
        insert child;
    }

    @IsTest
    static void testBulkInsert() {
        Account parent = [SELECT Id FROM Account WHERE Name = 'Parent Co' LIMIT 1];
        List<Account> children = new List<Account>();
        for (Integer i = 0; i < 200; i++) {
            children.add(new Account(Name = 'Child ' + i, ParentId = parent.Id));
        }
        Test.startTest();
        insert children;
        Test.stopTest();

        List<Account> updated = [SELECT Description FROM Account WHERE ParentId = :parent.Id];
        System.assert(!updated.isEmpty(), 'Children should have descriptions set');
        System.assert(updated[0].Description.startsWith('Child of:'), 'Description format mismatch');
    }
}

// Selective query — use indexed fields in WHERE clause
List<Opportunity> opps = [
    SELECT Id, Name, Amount, StageName
    FROM Opportunity
    WHERE AccountId IN :accountIds      // indexed field
      AND CloseDate >= :Date.today()    // indexed field
    ORDER BY CloseDate ASC
    LIMIT 200
];

// Relationship query to avoid extra round-trips
List<Account> accounts = [
    SELECT Id, Name,
           (SELECT Id, LastName, Email FROM Contacts WHERE Email != null)
    FROM Account
    WHERE Id IN :accountIds
];

<!-- counterComponent.html -->
<template>
    <lightning-card title="Counter">
        <div class="slds-p-around_medium">
            <p>Count: {count}</p>
            <lightning-button label="Increment" onclick={handleIncrement}></lightning-button>
        </div>
    </lightning-card>
</template>

// counterComponent.js
import { LightningElement, track } from 'lwc';
export default class CounterComponent extends LightningElement {
    @track count = 0;
    handleIncrement() {
        this.count += 1;
    }
}

<!-- counterComponent.js-meta.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>59.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__AppPage</target>
        <target>lightning__RecordPage</target>
    </targets>
</LightningComponentBundle>