Pass the Salesforce Developers PDII Questions and answers with ValidTests

The $Locale value provider should be used to ensure the Lightning application respects the user's locale for dates, times, numbers, currency, and currency symbols. This global value provider gives components access to locale formats and labels, which are automatically rendered according to the user's locale settings.References: Aura Components Developer Guide - $Locale Value Provider

The error occurs because DML operations were performed before a callout. To fix this, the callout should be made from an asynchronous method such as one annotated with @future(callout=true), which allows DML operations to be committed separately from the callout.References: Apex Developer Guide - Making Asynchronous Callouts

To test a Visualforce controller that works with specific records, you should insert the necessary test data in the test class. Then instantiate a PageReference for the Visualforce page, set the record id in the page parameters, and use System.currentPageReference().getParameters().put('id', recordId) to simulate navigating to the page with that record.References: Apex Developer Guide - Testing Custom Controllers and Controller Extensions

For optimizing queries, especially on large data volumes, it's recommended to use indexed fields such as External ID fields, which will make the queries selective. Among the options given:

B) is optimized because it is using the Customer_Number__c field, which is an External ID and hence indexed.

D) is also optimized because it filters out deleted records with IsDeleted = false and uses Name != ' ', which is likely to be selective.

Using indexed fields and filtering out unnecessary records helps in faster query execution on large data volumes.

References:

Make SOQL Query Selective

Working with Very Large SOQL Queries

Application Events in Aura components are used for communication between components that are not in the same containment hierarchy. An application event to alert users about the arrival of a guest at the front desk is appropriate because it allows any component within the app to listen and respond to the event, regardless of where it is located in the component hierarchy.References: Aura Components Developer Guide - Application Event

The correct SOQL query to retrieve all fields for a specific Account is to use the FIELDS(ALL) function within the SELECT clause of the SOQL query. This will return all fields for the Account named 'Acme'.References: SOQL and SOSL Reference Guide - FIELDS() Function

To improve the performance of an Aura component that is loading slowly, the developer can make the following change:

D. Change the default for showContactInfo to “False": By setting the default value of showContactInfo to False, the component does not fetch or render the contact information by default, which can reduce the initial load time. The information can be fetched and displayed later based on user action or other triggers.

Changing the type of contactInfo to "Map" (Option A) or moving the contents of <c:contactInfo> into the component (Option B) may not necessarily improve load times. Adding a change event handler for showContactInfo (Option C) adds more processing and can potentially slow down the component if not handled efficiently.

References:

Lightning Components Performance Best Practices: Improve Performance

When rolling back to a savepoint, any DML operations that occurred after that savepoint are undone, but static variables are not reverted. Therefore, when a rollback occurs, the state of all static variables at the time of the rollback remains the same as it was just before the rollback.References: Apex Developer Guide - Savepoint and Transaction Control

Custom metadata types are the best feature for storing variables that control style and behavior of a Lightning Web Component. Unlike custom settings, custom metadata is deployable and testable in both Production and all Sandboxes.References: Salesforce Help - Custom Metadata Types Overview

When developing a custom screen that requires both an Account and Contact to be created together, using setSavepoint() and rollback() within a try-catch block is a reliable way to ensure that if the Contact creation fails, the Account creation is also rolled back, maintaining data integrity.References: Apex Developer Guide - Savepoint and Transaction Control