moving insert to another model and done so in database internal

internal/handlers/portfolio.go

@@ -45,7 +45,7 @@ func AddTradeHandler(db *sql.DB) http.HandlerFunc {
 			Product:  model.TradeProduct(req.Product),
 			Type:     model.TradeType(req.Type),
 			Price:    req.Price,
-			Currency: currency,
+			Currency: currency.Name,
 			Date:     req.Date,
 		}