The JSON value could not be converted to System.Int32

Question

I want to send data of object to my Web API. The API accepts a parameter of class, which properties are type of int and string.

This is my class:

public class deneme
{
   public int ID { get; set; }
   public int sayi { get; set; }
   public int reqem { get; set; }
   public string yazi { get; set; }
}

This is my JSON object:

{
   "id":0,
   "sayi":"9",
   "reqem":8,
   "yazi":"sss"
}

I want the api read the property "sayi" as integer. but because it cant, it gives the error:

The JSON value could not be converted to System.Int32. Path: $.sayi

How could I solve this problem?

You can't assign a string value to an int variable, cast the string as int — FrV, Aug 23 '19 at 13:03
It's needs to be `"sayi": 9` (no quotes), or you must bind it to a string instead of an int, and convert it later yourself. No other option. — Chris Pratt, Aug 23 '19 at 13:23
before i updated from asp.net core 2.2 to 3.0 it worked when i type "9". after the update, it doesnt work. — ali suleymanli, Aug 23 '19 at 13:37
this could also be the error message when the number value is higher or lower than ints range, could be you need to define it as long, float, double etc.. just fyi for others googling this — alexfyren, Apr 08 '21 at 08:28
It is supported starting in .NET 5, please check an answer https://stackoverflow.com/a/67153702/3799228 — HRKoder, Apr 18 '21 at 21:50

score 101 · Answer 1 · answered Aug 26 '19 at 06:03

101

For Asp.Net Core 3.0, it uses System.Text.Json for serialization and deserialization.

For using old behavior, you could use Json.NET in an ASP.NET Core 3.0 project by referencing Json.NET support.

Short Answer:

Install Microsoft.AspNetCore.Mvc.NewtonsoftJson which is preview version.
Change to services.AddControllers().AddNewtonsoftJson();

answered Aug 26 '19 at 06:03

Edward

25,783
9
59
102

2

Perfect, thanks. Question is, why couldn't Microsoft just use the most downloaded NuGet package... – Adriaan Davel Nov 07 '19 at 07:03
2

It's not as efficient or performant. Newtonsoft is a great package as it covers a huge array of use-cases. With that large number of use-casts, comes performance overhead costs. Microsofts was very focused with theirs. It was performance driven for aspnetcore. – Johnathon Sullinger Nov 10 '19 at 06:35
2

I just had to go this route to get my object to deserialize properly. For some reason `Microsoft.AspNetCore.Mvc.NewtonsoftJson` doesn't show up in the package manager and had to manually install it with `Install-Package Microsoft.AspNetCore.Mvc.NewtonsoftJson -Version 3.0.0`. It'll indicate the package can be updated to 3.1.0, but it requires net core 3.1, which is still in prerelease as of writing this comment. Writing this in hopes it helps someone else who ran into this issue! – Zulukas Dec 03 '19 at 18:11

VahidN · Answer 2 · 2019-12-13T12:02:21.137

First you should create a JsonConverter for it:

using System;
using System.Buffers;
using System.Buffers.Text;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace sample_22_backend.Converters
{
    public class IntToStringConverter : JsonConverter<int>
    {
        public override int Read(ref Utf8JsonReader reader, Type type, JsonSerializerOptions options)
        {
            if (reader.TokenType == JsonTokenType.String)
            {
                ReadOnlySpan<byte> span = reader.HasValueSequence ? reader.ValueSequence.ToArray() : reader.ValueSpan;
                if (Utf8Parser.TryParse(span, out int number, out int bytesConsumed) && span.Length == bytesConsumed)
                {
                    return number;
                }

                if (int.TryParse(reader.GetString(), out number))
                {
                    return number;
                }
            }

            return reader.GetInt32();
        }

        public override void Write(Utf8JsonWriter writer, int value, JsonSerializerOptions options)
        {
            writer.WriteStringValue(value.ToString());
        }
    }
}

Then use it this way on your model's properties:

[JsonConverter(typeof(IntToStringConverter))]
public int GenreId { set; get; }

Or you can add it globally:

services.AddControllers()
        .AddJsonOptions(options => 
                options.JsonSerializerOptions.Converters.Add(new IntToStringConverter()));

Is there any non custom way to do this yet. I would think they would fix this and allow people to pass integers without quotes. This breaks many existing APIs. I think this is the best answer as I feel using Newtonsoft isn't moving forward in the right direction — Dan Parker, May 21 '20 at 21:06
It's scheduled for the next version of the .NET: https://github.com/dotnet/runtime/issues/30255 — VahidN, Jun 04 '20 at 04:08
You can also pass this as a part of the JsonSerializerOptions when calling the Deserialize method as such: var options = new JsonSerializerOptions { PropertyNameCaseInsensitive = true, Converters = { new API.Helpers.StringToGuidConverter() } }; StreamReader reader = new StreamReader(HttpContext.Current.Request.InputStream); string json = reader.ReadToEnd(); return JsonSerializer.Deserialize(json, options); — Sergio A., Oct 27 '21 at 20:34

score 14 · Answer 3 · answered Apr 18 '21 at 21:49

14

Starting in .NET 5, there is an option to deserialize numbers that are represented as JSON strings instead of throwing an exception.

using System.Text.Json;
using System.Text.Json.Serialization;

var options = new JsonSerializerOptions()
{
     NumberHandling = JsonNumberHandling.AllowReadingFromString |
     JsonNumberHandling.WriteAsString
};

// serialize
string denemeJson = JsonSerializer.Serialize<Deneme>(deneme, options);

// deserialize
Deneme denemeDeserialized = JsonSerializer.Deserialize<Deneme>(denemeJson, options);

answered Apr 18 '21 at 21:49

HRKoder

1,386
12
10

The name JsonNumberHandling doesnt exist on the actual context – Jhon Hernández Jul 21 '21 at 01:12
1

@JhonHernández Are you sure you're using .NET 5? – HRKoder Aug 11 '21 at 06:44
Upvoted. This is the answer for a .NET 5 project. – J Weezy Sep 14 '21 at 21:55

score 8 · Answer 4 · answered Apr 28 '20 at 15:49

In .NET CORE 3.X the serialize/deserialize process is done using System.Text.Json not Newtonsoft Json. Edward's answer did not work entirely for me:

Installing from Nuget Manager Microsoft.AspNetCore.Mvc.NewtonsoftJson won't make step 2 to compile.
Yes, add in Startup services.AddControllers().AddNewtonsoftJson(); - you will receive an error, AddNewtonsoftJson() not recognized.

At least this happened to me.

As a fix, uninstall what you've installed at step 1. In package manager console, run: Install-Package Microsoft.AspNetCore.Mvc.NewtonsoftJson -Version 3.0.0-preview8.19405.7 . This worked for me.

score 3 · Answer 5 · answered Jul 25 '20 at 04:35

3

Better parse the values to Integer and send data to Server Side application from your Client side application, This worked for me. Happy Coding!!

{
  "id":parseInt(0),
  "sayi":parseInt(9),
  "reqem":parseInt(8),
  "yazi":"sss"
 }

answered Jul 25 '20 at 04:35

Anglesvar

921
7
14

score 1 · Answer 6 · answered May 13 '20 at 22:40

1

in js model, make sure your values are formatted as parseFloat();

answered May 13 '20 at 22:40

Moustachio

174
5
23

score 1 · Answer 7 · answered Jul 11 '20 at 03:47

1

There is an another way: just create a DTO with the type string for number types and convert it into the controller or to the type that you need.

answered Jul 11 '20 at 03:47

Alejandro

89
1
2

Gsanto · Answer 8 · 2021-03-23T14:51:10.310

-3

May face this issue in .net core, You can change the datatype from int to int64

edited Mar 23 '21 at 14:51

answered Mar 23 '21 at 14:32

Gsanto

1
3

The JSON value could not be converted to System.Int32

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