Apex Trigger to update Parent record when any Child record is updated

 
Trigger to update parent record when any child record is updated.

  
When rollup summary cannot be used since the objects do not have a Master-Detail relationship, try the below:
 

trigger rollupKind on Child_Object__c (after insert, after delete, after update) {
    if(Trigger.isInsert){
            try {
                for (Child_Object__c child : Trigger.new){
                    Parent_Object__c parent = [SELECT Id, Sum_Field__c  FROM Parent_Object__c WHERE Id = :child.Parent_Lookup__c];
                    List<Child_Object__c> lChild = [SELECT Id, Amount__c FROM Child_Object__c WHERE Parent_Lookup__c = :parent.Id];
                    for(Child_Object__c amChild : lChild) {
                        amount += amChild.Amount__c; 
                    }
                    parent.Sum_Field__c = amount;
                    update parent;
                }
              } catch (Exception e) {
                  System.debug(e);
                }
        }
    if(Trigger.isAfter) {
        if(Trigger.isUpdate){
            try {
                for (Child_Object__c child : Trigger.old){
                    Parent_Object__c parent = [SELECT Id, Sum_Field__c  FROM Parent_Object__c WHERE Id = :child.Parent_Lookup__c];
                    List<Child_Object__c> lChild = [SELECT Id, Amount__c FROM Child_Object__c WHERE Parent_Lookup__c = :parent.Id];
                    for(Child_Object__c amChild : lChild) {
                        amount += amChild.Amount__c; 
                    }
                    parent.Sum_Field__c = amount;
                    update parent;
                }
               } catch (Exception e) {
                   System.debug(e);
                 }
        }
        if(Trigger.isDelete){
            try {
                for (Child_Object__c child : Trigger.old){
                    Parent_Object__c parent = [SELECT Id, Sum_Field__c  FROM Parent_Object__c WHERE Id = :child.Parent_Lookup__c];
                    List<Child_Object__c> lChild = [SELECT Id, Amount__c FROM Child_Object__c WHERE Parent_Lookup__c = :parent.Id];
                    for(Child_Object__c amChild : lChild) {
                        amount += amChild.Amount__c; 
                    }
                    parent.Sum_Field__c = amount;
                    update parent;
                }
               } catch (Exception e) {
                   System.debug(e);
                 }
        }
    }
}
 
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