Advanced 35 min read

Build the Selector Layer

By the end of this lesson, you'll be able to:

Write selector classes for Project__c and Milestone__c following Module 43's pattern
Design a selector method that supports the health-recalculation use case specifically
Apply WITH SECURITY_ENFORCED consistently across every selector

Prerequisites: "Build the Domain Layer"

ProjectSelector and MilestoneSelector

public with sharing class ProjectSelector {
    public Map<Id, Project__c> selectByIdAsMap(Set<Id> ids) {
        return new Map<Id, Project__c>([
            SELECT Id, Health__c, Status__c FROM Project__c WHERE Id IN :ids WITH SECURITY_ENFORCED
        ]);
    }
}

public with sharing class MilestoneSelector {
    public List<Milestone__c> selectByProjectIds(Set<Id> projectIds) {
        return [
            SELECT Id, Project__c, Status__c, Due_Date__c
            FROM Milestone__c
            WHERE Project__c IN :projectIds
            WITH SECURITY_ENFORCED
        ];
    }
}

Both follow Module 43\'s exact shape — one class per object, WITH SECURITY_ENFORCED on every query, methods named for what they select rather than exposing raw SOQL to callers.

A selector method shaped by its actual use case

selectByProjectIds exists specifically because MilestoneStatusService.recalculateProjectHealth (Lesson 5) needs every Milestone belonging to a given set of Projects, to determine whether any are overdue. The selector\'s method signature is designed around this concrete need, rather than being a generic "get everything" method — a deliberate, requirements-driven API, echoing Lesson 1\'s "requirements imply architecture" theme.

Consistency across every selector in the project

Every selector class in this project — for Project__c, Milestone__c, and the Support_Case__c/Time_Entry__c selectors built alongside them — applies WITH SECURITY_ENFORCED the same way, ensuring Module 28\'s security discipline is enforced uniformly across a data model spanning three departments, not just remembered in some places and forgotten in others.

Exercise

As a comment, explain why MilestoneSelector.selectByProjectIds takes a Set<Id> of Project IDs rather than a single Project Id.

Show hint

Think about how many projects a health-recalculation job might process in one run.

APEX

Build the Selector Layer Quiz

1. Why does every selector class in this project apply WITH SECURITY_ENFORCED the same way?

To ensure Module 28's security discipline is enforced consistently across a data model spanning three departments, rather than inconsistently applied WITH SECURITY_ENFORCED is only needed on Project__c, not the other objects It is optional and included here purely for decoration Selector classes cannot function without it, even outside security contexts

My Notes

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Summary

Two selector classes centralize every query this project needs against Project__c and Milestone__c — Module 43's exact selector pattern, applied to a data model with more inter-object relationships than the banking system had.

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