The JSON value could not be converted to System.Nullable[System.Int32]

Question

I updated an ASP.NET Core 2.2 API to ASP.NET Core 3.0 and I am using System.Json:

services
  .AddMvc()
  .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
  .AddJsonOptions(x => {})

I then tried to post JSON data using Angular 8, which was working before:

{
  "name": "John"
  "userId": "1"
}

The model in the ASP.NET Core 3.0 API is:

public class UserModel {
  public String Name { get; set; }
  public Int32? UserId { get; set; } 
}

And the API Controller action is as follows:

[HttpPost("users")]
public async Task<IActionResult> Create([FromBody]PostModel) { 
}

When I submit the model I get the following error:

The JSON value could not be converted to System.Nullable[System.Int32].

Do I need to do something else when using System.Json instead of Newtonsoft?

Does this answer your question? [JsonConverter equivalent in using System.Text.Json](https://stackoverflow.com/questions/56360401/jsonconverter-equivalent-in-using-system-text-json) — Orace, Nov 15 '19 at 22:42

Sandeep Kumar · Answer 1 · 2021-11-08T18:17:31.490

38

Microsoft has removed Json.NET dependency from ASP.NET Core 3.0 onwards and using System.Text.Json namespace now for serialization, deserialization and more.

You can still configure your application to use Newtonsoft.Json. For this -

Install Microsoft.AspNetCore.Mvc.NewtonsoftJson NuGet package
In ConfigureServices() add a call to AddNewtonsoftJson()-

services.AddControllers().AddNewtonsoftJson();

Read more on https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-apis/

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-migrate-from-newtonsoft-how-to

edited Nov 08 '21 at 18:17

answered May 22 '20 at 12:15

Sandeep Kumar

751
1
6
7

3

This is the more useful answer even if the accepted answer is correct for the question. – Mukus Oct 30 '20 at 00:38
it worked for me . Thanks – Sneha Aug 11 '23 at 09:41

MK Vimalan · Accepted Answer · 2019-11-15T22:35:57.303

12

Here Via the json you pass a string value for UserId but your model refer a int32? value for UserId. Then how your value convert from string to int32?

edited Nov 15 '19 at 22:35

answered Nov 15 '19 at 22:28

MK Vimalan

1,213
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4

I understand this but using Newtonsoft it was being converted ... I thing System.Json is more strict about it – Miguel Moura Nov 15 '19 at 22:30
1

Set json property atribute. – BASKA Nov 15 '19 at 22:49

score 2 · Answer 3 · answered Dec 25 '22 at 13:24

I faced this issue! and all those solutions did not work for me! so I did the following:-

First of all the data returned to me as the following:-

I need to make year as an int and also want to make value as double!
You should make custom JsonConverter, it worked for me after a lot of search, and here is sample of:-

StringToDoubleConverter

public sealed class StringToDoubleConverter : JsonConverter<double>
{
    public override double Read(
        ref Utf8JsonReader reader,
        Type typeToConvert, 
        JsonSerializerOptions options)
    {
        double.TryParse(reader.GetString(),out double value);
        return value;
    }

    public override void Write(
        Utf8JsonWriter writer,
        double value, 
        JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
}

Then you can save it to db! play around as you like

score 2 · Answer 4 · answered Feb 15 '23 at 10:49

2

In my scenario I was just sending the "", not the null :)

answered Feb 15 '23 at 10:49

Arekadiusz

419
4
11

The JSON value could not be converted to System.Nullable[System.Int32]

4 Answers4

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