Handle Overlapping Requests

List<Leave_Request__c> batch = new List<Leave_Request__c>{
    new Leave_Request__c(Employee_Name__c = 'Amara', Start_Date__c = Date.newInstance(2026, 3, 10), End_Date__c = Date.newInstance(2026, 3, 15)),
    new Leave_Request__c(Employee_Name__c = 'Amara', Start_Date__c = Date.newInstance(2026, 3, 12), End_Date__c = Date.newInstance(2026, 3, 20))
};
insert batch; // these two overlap each other — but neither exists in the database yet!

1. List<Leave_Request__c> batch = new List<Leave_Request__c>{ — two requests being submitted together.
2. new Leave_Request__c(Employee_Name__c = 'Amara', Start_Date__c = Date.newInstance(2026, 3, 10), End_Date__c = Date.newInstance(2026, 3, 15)), — the first.
3. new Leave_Request__c(Employee_Name__c = 'Amara', Start_Date__c = Date.newInstance(2026, 3, 12), End_Date__c = Date.newInstance(2026, 3, 20)) — the second, overlapping the first.
4. }; — closes the list literal.
5. insert batch; — these two overlap each other — but neither exists in the database yet. The previous lesson's check only compares against existingRequests (already-saved records) — it would miss this case entirely, since neither of these two new requests exists in the database yet to be found by that query.

for (Integer i = 0; i < newRequests.size(); i++) {
    for (Integer j = i + 1; j < newRequests.size(); j++) {
        Leave_Request__c reqA = newRequests[i];
        Leave_Request__c reqB = newRequests[j];

        Boolean sameEmployee = reqA.Employee_Name__c == reqB.Employee_Name__c;
        Boolean overlaps = datesOverlap(reqA.Start_Date__c, reqA.End_Date__c, reqB.Start_Date__c, reqB.End_Date__c);

        if (sameEmployee && overlaps) {
            reqB.Start_Date__c.addError('This request overlaps with another request in the same submission.');
        }
    }
}

1. for (Integer i = 0; i < newRequests.size(); i++) { — the outer loop.
2. for (Integer j = i + 1; j < newRequests.size(); j++) { — j = i + 1 (Module 7's classic-for-loop index control) ensures each pair of new requests is only compared once, never against itself.
3. Leave_Request__c reqA = newRequests[i]; — the first request in the pair.
4. Leave_Request__c reqB = newRequests[j]; — the second.
5. (blank line)
6. Boolean sameEmployee = reqA.Employee_Name__c == reqB.Employee_Name__c; — the same comparability check as before.
7. Boolean overlaps = datesOverlap(reqA.Start_Date__c, reqA.End_Date__c, reqB.Start_Date__c, reqB.End_Date__c); — this is the same overlap check from Lesson 3, applied to newRequests compared against itself instead of against existingRequests.
8. (blank line)
9. if (sameEmployee && overlaps) { — both conditions must be true.
10. reqB.Start_Date__c.addError('This request overlaps with another request in the same submission.'); — blocks the second request in the pair.
11. } — closes the if.
12. } — closes the inner loop.
13. } — closes the outer loop.

"This leave request overlaps with an existing request" and "This request overlaps with another request in the same submission" describe genuinely different situations — the first means a conflict with something already approved or pending; the second means the batch being submitted right now is internally inconsistent. Giving each its own specific message (Module 26's addError lesson) helps whoever's fixing the problem understand exactly what went wrong, rather than guessing.