How to Access a Value from a complex multi-relationship SOQL query?

Question

I have this monster of a query:

List<Case> updatedCases = [SELECT Id,ProductId, Vehicle__c, 
                               (SELECT Equipment__r.Maintenance_Cycle__c FROM Equipment_Maintenance_Items__r ORDER BY 
                                Equipment__r.Maintenance_Cycle__c ASC NULLS LAST LIMIT 1) FROM Case WHERE Id 
                             IN :cases AND (Type = 'Repair' OR Type = 'Routine Maintenance') AND 
                              Status = 'Closed'];

And I need to assign the value of the Maintenance_Cycle__c to a new case (in the Date_Due__c field) like so (except this one doesn't work):

 List<Case> newCases = new List<Case>();
    for(Case a:updatedCases){
        Case b = new Case();
        b.Type = 'Routine Maintenance';
        b.Vehicle__c = a.Vehicle__c;
        b.Subject = 'Routine Maintenance Request';
        b.Date_Reported__c = Date.today();
        b.Date_Due__c = Date.today() + updatedCases.get(Equipment__r.Maintenance_Cycle__c);
        newCases.add(b);
    }
    insert newCases;

How would I retrieve that value from my SOQL?

Answer 1

You can use the value from a:

if(a.Equipment_Maintenance_Items__r.size() == 1) {
  a.Due_Date__c = Date.today() + a.Equipment_Maintenance_Items__r[0].Equipment__r.Maintenance_Cycle__c;
}