Count of Child on Parent with Lookup Relation - Trigger

Here Child -> Buyers__c
              Parent -> oneplus__c

 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

trigger ChildCountOnParent on Buyers__c (After Insert,after Delete, After Update, After Undelete) { Set<Id> Parent_Set = New Set<Id>(); if(Trigger.isDelete || Trigger.isUpdate){ for(Buyers__c b : trigger.old){ Parent_Set.add(b.oneplus__c); } } if(Trigger.isInsert || Trigger.isUndelete || || Trigger.isUpdate){ for(Buyers__c b : trigger.new){ Parent_Set.add(b.oneplus__c); } } List<OnePlus__c> Parent_List = [Select id, Name,No_of_Buyers__c, (Select id, oneplus__c from buyers__r) from OnePlus__c WHERE ID IN :Parent_Set]; for(OnePlus__c one : Parent_List){ one.No_of_Buyers__c = one.buyers__r.size(); } Update Parent_List; }