Apex Trigger: Calculate the sum of child records field value and update in its parent object record field.

/* Name:UpdateParentTotalField
* Description: This trigger will calculate the sum of child records field values and update in its parent object record field. it will fire
* on both insert and update event.
*/

trigger UpdateParentTotalField on TestChild__c (after insert,after update) {
    
    set<id> prentsIds=new set<id>();
    if(Trigger.isInsert || Trigger.isUpdate){
        for(TestChild__c tc:Trigger.new){
            prentsIds.add(tc.TestParent__c);
        }
    }
    list<TestParent__c> parentList=new List<TestParent__c>();
    
    for(TestParent__c tp:[select id,Total_No__c,(select id,No__c from TestChilds__r) from TestParent__c where id IN:prentsIds]){
        TestParent__c obj=new TestParent__c();
        obj.id=tp.Id;
        for(TestChild__c tc:tp.TestChilds__r){
            if( obj.Total_No__c==null){
                obj.Total_No__c=0;
            }
            obj.Total_No__c+=tc.No__c;
        }
        parentList.add(obj);
    }
    if(parentList.size()>0){
        try{
            update parentList;
        }
        catch(DMLException e){
            system.debug('Exception has occured! ' +e.getMessage());
        }
    }
}