public IHttpActionResult Sell(TransactionDTO transaction)
 {
     if (ModelState.IsValid)
     {
         return Ok(_stockService.Sell(transaction.Ticker, transaction.Quantity, User.Identity.Name));
     }
     return BadRequest();
 }
        public IHttpActionResult Buy(TransactionDTO transaction)
        {

            if (ModelState.IsValid && _stockService.CheckExists(transaction.Ticker))
            {
                return Ok(_stockService.Buy(transaction.Ticker, transaction.Quantity, User.Identity.Name));
            }
            return BadRequest();

        }