Use JsonPatchDocument without Newtonsoft.Json

[rmja]

Describe the bug

The JsonPatchDocument does not specify a converter for the new System.Text.Json serializer and so any request to an action using JsonPatchDocument<T> returns a 400 model valutation error.

To Reproduce

Steps to reproduce the behavior:

1. Using this version of ASP.NET Core '3.0.0-preview7'
2. Use the System.Text.Json serializer, not Json.Net.
3. Make an action with parameter JsonPatchDocument<SomeModel>
4. Call the action with a simple patch, e.g. [{"op":"replace","path":"/number","value":115}].
5. See error 400 being returned

Expected behavior

Excpect the parameter to be correctly bound to the patch and a status 200.

Additional context

Include the output of dotnet --info

.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview7-012821
 Commit:    6348f1068a

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x86
 Base Path:   C:\Program Files (x86)\dotnet\sdk\3.0.100-preview7-012821\

Host (useful for support):
  Version: 3.0.0-preview7-27912-14
  Commit:  4da6ee6450

.NET Core SDKs installed:
  3.0.100-preview7-012821 [C:\Program Files (x86)\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.0.0-preview7.19365.7 [C:\Program Files (x86)\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.0.0-preview7-27912-14 [C:\Program Files (x86)\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview7-27912-14 [C:\Program Files (x86)\dotnet\shared\Microsoft.WindowsDesktop.App]

[rmja]

The following hack seems to work:
In Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
            var fakeServiceProvider = new ServiceCollection();
            fakeServiceProvider
                .AddLogging()
                .AddMvc()
                .AddNewtonsoftJson();

            var fakeMvcOptions = fakeServiceProvider.BuildServiceProvider().GetRequiredService<IOptions<MvcOptions>>().Value;

            services.AddMvc(options =>
                {
                    var jsonPatchInputFormatter = fakeMvcOptions.InputFormatters.OfType<Microsoft.AspNetCore.Mvc.Formatters.NewtonsoftJsonPatchInputFormatter>().Single();
                    options.InputFormatters.Insert(0, jsonPatchInputFormatter);
                });
}

Is there any more elegang way to accomplish JsonPatch support?

[mkArtakMSFT]

Thanks for contacting us, @rmja.
We don't support JSONPatch without Newtonsoft.Json.
You can simply call .AddNewtonsoftJson() on the service collection instance.

[rmja]

@mkArtakMSFT year, but that replaces the System.Text.Json formatter for all json which is really unfortunate. How do I use Json.Net only for application/json-patch+json requests in a more clean way than my example above?

[dhhunter]

A PATCH request to WebAPI always returns an UnsupportedMediaType Response. Taking a dependence on Newtonsoft.Json (and calling AddNetwtonsoftJson()) does not change that. I have tried decorating the method with a Consumes attribute, writing my own custom InputFormatter (which appear to be broken in general), even changing the ContentType Header to a media type that should be supported (IE: application\json), nothing seems to work.

[mkArtakMSFT]

@rmja your original code is actually the way to go in that case.

@dhhunter your concerns are unrelated to this topic. Please file a separate issue if you want, and we will look into that separately.