public async Task <IActionResult> Import(IFormFile file) { if (file == null) { return(Content("Error: File is null")); } string fileExtension = Path.GetExtension(file.FileName); if (fileExtension != ".xls" && fileExtension != ".xlsx") { return(Content("Error: Wrong file extension")); } var stream = file.OpenReadStream(); List <Contract> contracts = await Task.Run(() => { ExcelHandler excelHandler = new ExcelHandler(stream, fileExtension); return(excelHandler.GetContractsFromExcel()); }); DBContext dBContext = new DBContext(); await dBContext.Contracts.AddRangeAsync(contracts); await dBContext.SaveChangesAsync(); return(Content("All good")); }