Intermediate 25 min read

Deduplicate and Validate (Sets)

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

Use a Set to list every unique department across all employees
Reject an employee with a duplicate employee ID before adding
Explain why validation belongs inside addEmployee, not scattered across callers

Prerequisites: "Model an Employee Directory (Maps)"

Listing unique departments

public Set<String> getAllDepartments() {
    Set<String> departments = new Set<String>();
    for (Employee emp : employeesById.values()) {
        departments.add(emp.getDepartment());
    }
    return departments;
}

employeesById.values() returns every Employee in the map (ignoring the keys); looping over them and adding each department to a Set automatically deduplicates — exactly Module 16's "Sets" lesson, applied directly to real employee data.

Rejecting a duplicate employee ID

public Boolean addEmployee(Employee emp) {
    if (employeesById.containsKey(emp.getEmployeeId())) {
        System.debug('Employee ID ' + emp.getEmployeeId() + ' already exists.');
        return false;
    }
    employeesById.put(emp.getEmployeeId(), emp);
    return true;
}

containsKey() checks whether the ID is already taken before adding — without this check, a second put() with the same key would silently overwrite the original employee, losing their data entirely. addEmployee now returns a Boolean, exactly the pattern from Module 12's "Add Business Rules" lesson.

Why this validation lives inside addEmployee

It would be possible to check for duplicates separately, everywhere addEmployee gets called — but exactly like Module 12's CourseRoster.enroll(), that means every caller has to remember to repeat the check, and any caller that forgets creates a silently corrupted directory. Putting the rule inside addEmployee itself enforces it everywhere, automatically.

Exercise

Add a method hasEmployeesInDepartment(String department) that returns true if any employee belongs to that department, using getAllDepartments().

Show hint

return getAllDepartments().contains(department);

APEX

Deduplicate and Validate (Sets) Quiz

1. What would happen without the containsKey() check before adding an employee?

A second employee with the same ID would silently overwrite the first, losing their data Apex would throw a compile error Both employees would be stored under the same key somehow Nothing — Maps prevent this automatically

My Notes

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Summary

This lesson adds two Set-backed capabilities: listing every unique department, and rejecting a duplicate employee ID before it corrupts the directory.

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