Cannot replace default JSON contract resolver in ASP.NET Core 3 - asp.net-core

Question

After creating basic Web API project based on .NET Core 3.0 framework, all API responses were coming in camel case. I installed SwashBuckle Swagger + built-in JSON serializer from System.Text.Json, specifically, to display enums as strings, everything worked as before. Then, I decided to switch to NSwag + NewtonSoftJson, because of some limitations of built-in serializer with dynamic and expando objects. Now, all API responses are displayed in PascalCase and I cannot change neither naming policy, nor even create custom contract resolver.
Example
https://forums.asp.net/t/2138758.aspx?Configure+SerializerSettings+ContractResolver
Question
I suspect that maybe some package overrides contract resolver behind the scene. How to make sure that API service uses ONLY custom contract resolver that I assign at startup and ignores all other similar settings?
Custom JSON contract resolver:
public class CustomContractResolver : IContractResolver
{
private readonly IHttpContextAccessor _context;
private readonly IContractResolver _contract;
private readonly IContractResolver _camelCaseContract;
public CustomContractResolver(IHttpContextAccessor context)
{
_context = context;
_contract = new DefaultContractResolver();
_camelCaseContract = new CamelCasePropertyNamesContractResolver();
}
// When API endpoint is hit, this method is NOT triggered
public JsonContract ResolveContract(Type value)
{
return _camelCaseContract.ResolveContract(value);
}
}
Controller:
[ApiController]
public class RecordsController : ControllerBase
{
[HttpGet]
[Route("services/records")]
[ProducesResponseType(typeof(ResponseModel<RecordEntity>), 200)]
public async Task<IActionResult> Records([FromQuery] QueryModel queryModel)
{
var response = new ResponseModel<RecordEntity>();
return Content(JsonConvert.SerializeObject(response), "application/json"); // NewtonSoft serializer
}
}
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
services
.AddCors(o => o.AddDefaultPolicy(builder => builder
.AllowAnyOrigin()
.AllowAnyHeader()
.AllowAnyMethod()));
services
.AddControllers(o => o.RespectBrowserAcceptHeader = true)
/*
.AddJsonOptions(o =>
{
o.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
o.JsonSerializerOptions.DictionaryKeyPolicy = JsonNamingPolicy.CamelCase;
o.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
})
*/
.AddNewtonsoftJson(o =>
{
o.UseCamelCasing(true);
o.SerializerSettings.Converters.Add(new StringEnumConverter());
//o.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver { NamingStrategy = new CamelCaseNamingStrategy() };
o.SerializerSettings.ContractResolver = new CustomContractResolver(new HttpContextAccessor());
});
services.AddOpenApiDocument(o => // NSwag
{
o.PostProcess = document =>
{
document.Info.Version = "v1";
document.Info.Title = "Demo API";
};
});
DataConnection.DefaultSettings = new ConnectionManager(DatabaseOptionManager.Instance); // LINQ to DB
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
app.UseCors(o => o.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader());
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(o => o.MapControllers());
app.UseOpenApi(); // NSwag
app.UseSwaggerUi3(o => o.Path = "/v2/docs");
app.UseReDoc(o => o.Path = "/v1/docs");
}

Answer 1

Still don't understand why custom contract resolver is not triggered by API endpoint, but found a combination that works for me to switch API to camel case. Feel free to explain why it works this way.
services.AddControllers(o => o.RespectBrowserAcceptHeader = true)
// Options for System.Text.Json don't affect anything, can be uncommented or removed
//.AddJsonOptions(o =>
//{
// o.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
// o.JsonSerializerOptions.DictionaryKeyPolicy = JsonNamingPolicy.CamelCase;
// o.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
//})
.AddNewtonsoftJson(o =>
{
o.UseCamelCasing(true);
o.SerializerSettings.Converters.Add(new StringEnumConverter());
// This option below breaks global settings, so had to comment it
//o.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver
//{
// NamingStrategy = new CamelCaseNamingStrategy()
//};
});
JsonConvert.DefaultSettings = () => new JsonSerializerSettings
{
ContractResolver = new CamelCasePropertyNamesContractResolver()
};
Idea was taken from this article.
NewtonSoft allows to set global serialization settings disregarding MVC, Web API, and other frameworks.