Hi Developers,

Can anyone help me on this issue, I have a Child object that has a Lookup to Parent. I wrote the below apex class and the trigger on child, such that the count of Child records should be shown on each Parent record. I have a number field on the Parent which should be update as per the Trigger.

It works fine except in one scenario, it does not consider the existing Child records on the Parent, hence it shows incorrect count on the Parent record. It works perfect if I add the new Child records. I heard that Batch Apex can resolve this issue, I am not sure how Batch Apex is related here to resolve the isssue. Can I get some guidance here to proceed further.


Any help on this is much appreciated.
Thank you.

Apex Class:

public class ChildCountHelper{
    
    //List<Parent__c> parentList = [select id, child_count__c, (select id from child__r) from Parent__c where id in :parentIDSet];
    
    public List<ID> conList= new List<ID>();
    
    public static void handleBeforeInsert(List<Child__c> childList){
        Set<ID> parentIDSet = new Set<ID>();
        
        for(Child__c childRec: childList){
     
            parentIDSet.add(childRec.Parent__c);
            
        }
        
        Map<ID, Parent__c> parentMap = new map<ID, parent__c>([select id, child_count__c from Parent__c where id in :parentIDSet]);
        for(Child__c childRec: childList){
            if(parentMap.get(childRec.Parent__c).child_count__c == null){
                parentMap.get(childRec.Parent__c).child_count__c = 0;
            }
            parentMap.get(childRec.Parent__c).child_count__c ++;
        }
        update parentMap.values();
    }
    
    public static void handleBeforeUpdate(List<Child__c> newChildList, List<Child__c> oldChildList){
        Set<ID> parentIDSet = new Set<ID>();
        Map<ID, ID> oldChildMap = new Map<ID, ID>();
        
        for(Child__c childRec: newChildList){
            parentIDSet.add(childRec.Parent__c);
        }
        
        for(Child__c childRec: oldChildList){
            parentIDSet.add(childRec.Parent__c);
            oldChildMap.put(childRec.Id, childRec.Parent__c);
        }
        
        Map<ID, Parent__c> parentMap = new map<ID, parent__c>([select id, child_count__c from Parent__c where id in :parentIDSet]);
        for(Child__c childRec: newChildList)
       {
        /*if(ChildRec.Parent__c!=null){  */
            if(parentMap.get(childRec.Parent__c).child_count__c == null){
                parentMap.get(childRec.Parent__c).child_count__c = 0;
            }
           // }
            if(childRec.Parent__c != oldChildMap.get(childRec.id)){
                if(oldChildMap.get(childRec.id) == null && childRec.Parent__c != null){
                    parentMap.get(childRec.Parent__c).child_count__c ++;
                }else if(oldChildMap.get(childRec.id) != null && childRec.Parent__c == null){
                    parentMap.get(oldChildMap.get(childRec.id)).child_count__c --;
                }else if(oldChildMap.get(childRec.id) != null && childRec.Parent__c != null){
                    parentMap.get(oldChildMap.get(childRec.id)).child_count__c --;
                    parentMap.get(childRec.Parent__c).child_count__c ++;
                }
            }
            
        }
        update parentMap.values();
    }
    
    public static void handleBeforeDelete(List<Child__c> childList){
        Set<ID> parentIDSet = new Set<ID>();
        for(Child__c childRec: childList){
            parentIDSet.add(childRec.Parent__c);
        }
        
        Map<ID, Parent__c> parentMap = new map<ID, parent__c>([select id, child_count__c from Parent__c where id in :parentIDSet]);
        for(Child__c childRec: childList){
            if(parentMap.get(childRec.Parent__c).child_count__c == null){
                parentMap.get(childRec.Parent__c).child_count__c = 0;
            }
            parentMap.get(childRec.Parent__c).child_count__c --;
        }
        update parentMap.values();
    }
    
    public static void handleBeforeUnDelete(List<Child__c> childList){
        Set<ID> parentIDSet = new Set<ID>();
        for(Child__c childRec: childList){
            parentIDSet.add(childRec.Parent__c);
        }
        
        Map<ID, Parent__c> parentMap = new map<ID, parent__c>([select id, child_count__c from Parent__c where id in :parentIDSet]);
        for(Child__c childRec: childList){
            if(parentMap.get(childRec.Parent__c).child_count__c == null){
                parentMap.get(childRec.Parent__c).child_count__c = 0;
            }
            parentMap.get(childRec.Parent__c).child_count__c ++;
        }
        update parentMap.values();
    }

}




Trigger:


trigger ChildTrigger on Child__c (before insert, after update, after delete, after undelete) {
    if (Trigger.isInsert) {
        ChildCountHelper.handleBeforeInsert((List<Child__c>)Trigger.NEW);
    }else if (Trigger.isUpdate) {
        ChildCountHelper.handleBeforeUpdate((List<Child__c>)Trigger.NEW, (List<Child__c>)Trigger.OLD);
    }else if (Trigger.isDelete) {
        ChildCountHelper.handleBeforeDelete((List<Child__c>)Trigger.OLD);
    }else if (Trigger.isUndelete) {
        ChildCountHelper.handleBeforeUnDelete((List<Child__c>)Trigger.NEW);
    }
}