Set Default Global JSON Serializer Settings

Set default global json serializer settings

Setting the JsonConvert.DefaultSettings did the trick.

JsonConvert.DefaultSettings = () => new JsonSerializerSettings
{
    Formatting = Formatting.Indented,
    TypeNameHandling = TypeNameHandling.Objects,
    ContractResolver = new CamelCasePropertyNamesContractResolver()
};

How to globally set default options for System.Text.Json.JsonSerializer?

No, JsonSerializerOptions does not expose the default options. If you are using a particular web framework there may be a way to specify (de-)serialization settings through that. Otherwise, I suggest creating your own convenience methods.

See also this open issue.

How to set json serializer settings in asp.net core 3?

AddMvc returns an IMvcBuilder implementation, which has a corresponding AddJsonOptions extension method. The new-style methods AddControllers, AddControllersWithViews, and AddRazorPages also return an IMvcBuilder implementation. Chain with these in the same way you would chain with AddMvc:

services.AddControllers()
    .AddJsonOptions(options =>
    {
        // ...
    });

Note that options here is no longer for Json.NET, but for the newer System.Text.Json APIs. If you still want to use Json.NET, see tymtam's answer

Json.net global settings

So, this was added to Json.net 5.0 Release 5

JsonConvert.DefaultSettings = () => new JsonSerializerSettings
{
    DateTimeZoneHandling = DateTimeZoneHandling.Local
};

From the release notes:

Set once with JsonConvert.DefaultSettings in an application, the default settings will automatically be used by all calls to JsonConvert.SerializeObject/DeserializeObject, and JToken.ToObject/FromObject. Any user supplied settings to these calls will override the default settings.

Because there are cases where JSON should not be customized, e.g. a Facebook or Twitter library, by default JsonSerializer won’t use DefaultSettings, providing an opt-out for those frameworks or for places in your application that shouldn’t use default settings. To create a JsonSerializer that does use them there is a new JsonSerializer.CreateDefault() method.

Do note that when ASP.NET invokes Newtonsoft directly, e.g. in model binding or response formatting, it opts out of using these global default settings. To configure defaults used internally by ASP.NET see this answer by Andrei.

Setting defaults for JsonContent in Asp.Net Core

As far as I know, there is no option for telling JsonContent.Create() to use the global JsonSerializerOptions.

BUT you could use the options pattern to retrieve the global JsonSerializerOptions, you've added with AddJsonOptions(...);.

Program.cs:

builder.Services.AddControllers().AddJsonOptions(options =>
{
    options.JsonSerializerOptions.PropertyNamingPolicy = null;
});

Options injected in Controller:

private readonly IOptions<JsonOptions> _JsonOptions;

public YourController(IOptions<JsonOptions> options)
{
    _JsonOptions = options;
}

...

// in your request method:
using var request = new HttpRequestMessage(HttpMethod.Post, "myrequest");
using var content = new MultipartFormDataContent
{
    { new StreamContent(image), "data", "file.ext" },
    { JsonContent.Create(wfc, null, JsonOptions.Value.JsonSerializerOptions), "Object" }
};
request.Content = content;
using var res = await _httpClient.SendAsync(request);

...

To simplify things a bit more, you could use a static helper method, so you don't need to pass the type and you can just pass the options.

PascalCaseHelper.cs:

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;

using System.Net.Mime;
using System.Text;
using System.Text.Json;

namespace YourNamespace
{
    public static class PascalCaseHelper
    {
        public static StringContent CreateJson(object data, IOptions<JsonOptions> options)
        {
            return new StringContent(
                JsonSerializer.Serialize(data, options.Value.JsonSerializerOptions), 
                Encoding.UTF8,
                MediaTypeNames.Application.Json);
        }
    }
}

// Usage:
{ PascalCaseHelper.CreateJson(myObject, _JsonOptions), "Object" }

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