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

Question

json serializer settings for legacy asp.net core applications were set by adding AddMvc().AddJsonOptions(), but I don\'t use AddMvc() in asp.

Answer 1

Option A. AddControllers

This is still MVC, and requires Microsoft.AspNetCore.Mvc.NewtonsoftJson nuget package, but you said you use AddControllers.

From Add Newtonsoft.Json-based JSON format support

services.AddControllers().AddNewtonsoftJson(options =>
{
    // Use the default property (Pascal) casing
    options.SerializerSettings.ContractResolver = new DefaultContractResolver();

    // Configure a custom converter
    options.SerializerOptions.Converters.Add(new MyCustomJsonConverter());
});

---

Option B. DefaultSettings

JsonConvert.DefaultSettings = () => new JsonSerializerSettings (...)

JsonConvert.DefaultSettings Property

Gets or sets a function that creates default JsonSerializerSettings. Default settings are automatically used by serialization methods on JsonConvert, and ToObject () and FromObject(Object) on JToken. To serialize without using any default settings create a JsonSerializer with Create().

Answer 2

Adding Newtonsoft is not necessary, quite a problems with adding Newtonsoft compatibility packages on .Net Core 3.0 project.

See also https://github.com/aspnet/AspNetCore/issues/13564

Of course, one would celebrate property naming PascalCase, NA at the moment... So null for PropertyNamingPolicy means PascalCase, which is obviously not very good.

// Pascal casing
services.AddControllersWithViews().
        AddJsonOptions(options =>
        {
            options.JsonSerializerOptions.PropertyNameCaseInsensitive = true;
            options.JsonSerializerOptions.PropertyNamingPolicy = null;
        });

Answer 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