public Class checkRecursive{
    private static boolean run = true;
    public static boolean runOnce(){
    if(run){
     run=false;
     return true;
    }else{
        return run;
    }
    }
}


trigger NoOfAttch on Attachment (after insert, after update, after delete) {
    if(checkRecursive.runOnce()) {
        if(Trigger.isupdate || Trigger.isInsert) {
			List<Id> accIds = new List<Id>();
			List<Id> accIdsupd = new List<Id>();
			Set<Id> ids=Trigger.newmap.keyset();
			Map<String,Integer> mapIds = new Map<String,Integer>();
        
			for(Attachment att : trigger.new) {
				accIds.add(att.ParentId);
			}
    
    
			List<aggregateResult> aggres = [SELECT ParentId,count(Id) FROM Attachment WHERE ParentId IN : accIds GROUP BY ParentId];
        
			for(AggregateResult aggr : aggres) {
				mapIds.put(string.valueof(aggr.get('ParentId')), integer.valueOf(aggr.get('expr0')));
			}

        
			for(Attachment attch : Trigger.new) {
				accIdsupd.add(attch.ParentId);
			}
        
			List<Account> accList = [SELECT Id, Number_of_attachments__c FROM Account WHERE Id IN : accIdsupd];
    
			for(Account accnt : accList) {
				accnt.Number_of_attachments__c = mapIds.get(accnt.Id);
			}
			update accList;
        }
        
		if(trigger.isdelete) {
			//Integer noOfrecords = [SELECT count() FROM Attachment WHERE Id IN :Trigger.newMap.keySet()];
        	List<Id> accDel = new List<Id>();
            for(Attachment att : Trigger.old) {
                accDel.add(att.ParentId);
            }
            List<Account> accListDel = [SELECT Id, Number_of_attachments__c FROM Account WHERE Id IN : accDel];
            for(Account acc : accListDel) {
                acc.Number_of_attachments__c = acc.Number_of_attachments__c - 1;
            }
            update accListDel;
		}
    }

}