Assigning operators for Date fields and comparing with today(), Scheduled Apex Code

Question

Exam_Date__c = 01/01/2018, Expiration_Date__c = 01/31/2018 (usually 30 days gap)

I want to send an email 7 days prior to expiration, on say eg. 01/25/2018, likewise.

I used the following formula in my apex code

if (Expiration_Date__c -7 <= Today() AND Today() < Expiration_Date__c) {sets a checkbox to true, and that checkbox value is checked by a process which sends an email}

This code is sending emails to all the exams that have been created, I don't understand why. Even the ones that have expiration dates two months ahead.

global class examExpiryAlert implements Schedulable {
    global void execute(SchedulableContext ctx) {
        List<Exam__c> objects = [
            SELECT Name, Exam_state__c, Expiration_Date_WF__c, day7Alert__c 
            FROM Exam__c
            WHERE Exam_state__c = 'Active'];

        for(Exam__c e : objects){
            if(e.Expiration_Date_WF__c - 7 <= Date.Today() && e.Expiration_Date_WF__c > Date.Today()) {  
                e.day7Alert__c = True;
            } 
        }
        update objects;
    }
}

Answer 1

try with:

        if(e.Expiration_Date_WF__c.addDays(-7) == Date.Today() && e.Expiration_Date_WF__c > Date.Today()) {  
            e.day7Alert__c = True;
        }