for(object__c conv: database.query(query)){
            List <Attachment> attachmentList = [SELECT Id, Name, ContentType, ParentId FROM Attachment WHERE ParentId = :conv.Id limit 1];
            if (attachmentList.size() > 0){
                Attachment att = attachmentList[0];
                row.AttachmentId = att.Id;
                row.AttachmentName = att.Name;
                row.AttachmentType = att.ContentType;
            }

list <Attachment> attachmentList = [select Id, Name, ParentId from Attachment];
        for(object__c conv: database.query(query)){
            for (Attachment att : attachmentList){
                if (conv.Id == att.ParentId){
                    row.AttachmentId = att.Id;
                    row.AttachmentName = att.Name;
                    row.AttachmentType = att.ContentType;
                }
            }