Updating related record in update trigger

Question

I'm stuck in the following issue:

there is a DB with Reference__c custom object with fields: AccountId, ContactId, IsPrimary(Boolean). There can be only one Reference with isPrimary=true for a one separate Contact.

A task is - when a user changes isPrimary value from False to True in a Reference object, a trigger must update the isPrimary value from True to False on one of related Reference records (last created, for example) with the same ContactId. At the same time user cannot update isPrimary value from True to False manually.

Is there a solution for this task so that I do not use a global static variable?

Currently, the update method in handler looks like:

public static void onAfterUpdate (Trigger.new, Trigger.oldMap) {

        List<Reference__c> afterUpdateList = [SELECT Id, Name, isPrimary__c, Contact__c, CreatedDate FROM Reference__c ORDER BY CreatedDate DESC];

        Set<Id> contIds = new Set<Id>();

        for (Reference__c ref: Trigger.new) {
            contIds.add(ref.Contact__c);
        }

        List<Reference__c> updateList = new List<Reference__c>();

        for (Reference__c ref: Trigger.new) {

            Boolean newContIsPrimary = ref.isPrimary__c;
            Boolean oldContIsPrimary = oldMap.get(ref.Id).isPrimary__c;

            if (!oldContIsPrimary && newContIsPrimary) {

                for (Reference__c r: afterUpdateList) {

                    if (r.Id != ref.Id && r.Contact__c == ref.Contact__c && r.isPrimary__c) {

                        r.isPrimary__c = false;

                        updateList.add(r);

                        break;

                    } 

                }

            } else if (oldContIsPrimary && !newContIsPrimary) {

                ref.addError('UPDATE_TO_FALSE_ERROR_MESSAGE');

            } 

        }

        if (!updateList.isEmpty()) {

            update updateList;

        }

    }

But it does not work properly as far as it does not distinct the context whether the user makes updates himself or the update is performed by the trigger.

Answer 1

A public static variable would be the best way to do this - your requirement is a load of ........

The only other way to do this without a static variable is to:

1. Add a checkbox field to the object named say "Trigger Executed"
2. Make it read only to everyone

3. In the trigger

    for (Reference__c r: afterUpdateList) {
   
               if (r.Id != ref.Id && r.Contact__c == ref.Contact__c && r.isPrimary__c) {
   
                   r.isPrimary__c = false;
                   r.Trigger_Executed__c = true;
                   updateList.add(r);
   
                   break;
   
               } 
   
           }
   

Then have a WFR that sets the value of Trigger_Executed__C to false if it is true (Which will happen after the trigger) - This is a lesson in order of execution