ASP.NET Core -- Upload .json file and convert to List<T>

Question

So I managed to export a .json file by serializing my List. Now i'm trying to upload a .json file and desearialize it and add it back to my list. The idea is to be able to click on import, choose a file, then convert it so i can add it to my list. Here is the function in my controller that doesn't work:

** Update ** So now I managed to convert the .json file back to my List but if the list is empty and I want to add the new list to it, then I get this error:

[HttpPost]
    public async Task<IActionResult> Import(IFormFile file)
    {
        if (file == null || file.Length == 0)
            return Content("file not selected");

        var path = Path.Combine(Directory.GetCurrentDirectory(), "Import", file.FileName);

        using (var stream = new FileStream(path, FileMode.Create))
        {
            await file.CopyToAsync(stream);
        }

        String jsonImport = System.IO.File.ReadAllText(path);
        Console.WriteLine(jsonImport);
        List<Booking> bookings;
        _cache.TryGetValue("key", out bookings);
        List<Booking> newList = new List<Booking>();

        newList = JsonConvert.DeserializeObject<List<Booking>>(jsonImport);

        foreach (var item in newList)
        {
            bookings.Add(item);
            _cache.Set<List<Booking>>("key", bookings);
        }
        return RedirectToAction("Index");
    }

So I want to choose a file (user should only be allowed to upload .json format nothing else but idk how to do that yet) and then from that .json I want to add every entry to my bookings List. Here is the Booking Model:

public class Booking
{
    [Required]
    [Display(Name = "Ladestand")]
    [Range(0, 100)]
    public double chargeState { get; set; }

    [Required]
    [Display(Name = "Benötigte Fahrstrecke")]
    [Range(1, 1000)]
    public double distance { get; set; }

    [Required]
    [Display(Name = "Beginn")]

    public DateTime startTime { get; set; }

    [Required]
    [Display(Name = "Ende")]

    public DateTime endTime { get; set; }

    [Required]
    [Display(Name = "Anschlusstyp")]
    [EnumDataType(typeof(ConnectorType))]
    public ConnectorType connectorType { get; set; }
}

And here is the export function:

public ActionResult Export()
    {
        string fileName = "BookingsExport.json";
        List<Booking> bookingsList;
        _cache.TryGetValue("key", out bookingsList);

        string json = JsonConvert.SerializeObject(bookingsList);
        FileInfo file = new FileInfo(fileName);
        using (StreamWriter writer = file.CreateText())
        {
            writer.Write(json);
        }

        byte[] fileBytes = System.IO.File.ReadAllBytes(fileName);

        return File(fileBytes, System.Net.Mime.MediaTypeNames.Application.Json, fileName);
    }

function in my controller that doesn't work is not a description of your problem. Do you have an error message to share? — Steve
– Steve, Commented May 28, 2020 at 19:31
Sorry my bad: Error CS0266 Cannot implicitly convert type 'object' to 'System.Collections.Generic.List<WebApplication.Models.Booking>'. An explicit conversion exists (are you missing a cast?) — Compil3
– Compil3, Commented May 28, 2020 at 19:39
So basically the problem is with the newList = JsonConvert.DeserializeObject(jsonImport); I don't know how to convert the .json file back to List<Booking> — Compil3
– Compil3, Commented May 28, 2020 at 19:40
ok i'm a bit confused like it seemed to work, BUT...if i open the web application, my list is empy by default then i import a list it doesn't work. If i add something to my list so that it's not empty before importing then it works. how can i add a png file to show you the problem ? — Compil3
– Compil3, Commented May 28, 2020 at 19:48

ProV · Accepted Answer · 2020-05-28 20:01:56Z

1

You need to initialize the list, before you are trying to add new items to it.

var bookings = new List<Booking>();

answered May 28, 2020 at 20:01

ProV

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Comments

Rena · Accepted Answer · 2020-05-29 03:24:09Z

1

That is because if you do not has value in the cache,it would set the value null to the bookings.You need to change like below:

List<Booking> bookings;
var flag = _cache.TryGetValue("key", out bookings);
if(!flag)
{
    bookings = new List<Booking>();
}

answered May 29, 2020 at 3:24

Rena

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