private DbHolder ToDbHolder(DTOHolder item)
        {
            var holder   = _bankContext.Holders.Find(item.Id) ?? throw new InvalidOperationException("Holder not found, incorrect id!");
            var accounts = ToAccounts(item.Accounts);

            return(HolderMapper.UpdateDbHolder(item, holder, accounts));
        }
        public void Add(DTOHolder item)
        {
            var holder = new DbHolder
            {
                Id = item.Id
            };
            var accounts = ToAccounts(item.Accounts);

            holder = HolderMapper.UpdateDbHolder(item, holder, accounts);
            _bankContext.Holders.Add(holder);
        }