Count of grand-Child Object records and Update them in Parent Field when they have lookup-relationship among them

Question

I'm creating a trigger to update the total number of opportunity-line-items in Account record, but my code isn't working as i have 1 Account record with multiple Opportunity records, for each opportunity record we have multiple opportunity line item records.

Need the count of all the opportunityLineItems that are associated with all the opportunities for an account.

...
trigger countOfOli on OpportunityLineItem (after insert) {
  Set<Id> accountIds = new Set<Id>();
   Set<Id> oppIds= new Set<Id>();
   
   for(OpportunityLineItem  ol: trigger.new){
     oppIds.add(ol.OpportunityId);
   }
    
   Map<Id,Opportunity> oppMap = new Map<Id,Opportunity>([select AccountId, (select Id from OpportunityLineItems) from Opportunity where id in:oppIds]); 
    system.debug('Opp Map'+ oppMap.values());
    set<Id> accIds = new Set<Id>();
    for(Opportunity opp: oppMap.values()){
        accIds.add(opp.AccountId);
    }
    Map<Id, Account> accMap = new  Map<Id, Account>([select Id, Number_of_Contacts__c from Account where Id in:accIds]);
    for(OpportunityLineItem opli: trigger.new){
        if(oppMap.containsKey(opli.OpportunityId) && accMap.containsKey(oppMap.get(opli.OpportunityId).AccountId)){
            accMap.get(oppMap.get(opli.OpportunityId).AccountId).Number_of_Contacts__c = oppMap.get(opli.OpportunityId).OpportunityLineItems.size();
        }
    }
    update accMap.values();   
}
...

Answer 1

Your trigger is overly complicated. All you need is:

Map<Id, Account> accounts = new Map<Id, Account>();
for(Opportunity record: Trigger.new) {
  accounts.put(record.AccountId, new Account(Id=record.AccountId, Total_Line_Items__c=0));
}
for(AggregateResult result:[SELECT COUNT(Id) sum, Opportunity.AccountId accountId FROM OpportunityLineItem WHERE Opportunity.AccountId = :accounts.keySet() GROUP BY Opportunity.AccountId]) {
  Id accountId = (Id)result.get('accountId');
  Integer sumCount = (Integer)result.get('sum');
  accounts.get(accountId).Total_Line_Items__c = sumCount;
}
update accounts.values();