c# - Using Nswag with Odata creates error when try to access swagger endpoint

Question

We are trying to use Nswag and Odata both in our asp.net core API project. We can either Nswag for API documentation or Odata for query simplification. But when we use both of them and try to access API swagger document (https://localhost:5001/swagger/index.html) it's generating this error:

Here's my Startup Files:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;


using Microsoft.AspNet.OData.Extensions;
using System.Web.Http;
using Microsoft.OpenApi.Models;
using System.Reflection;
using Newtonsoft.Json;
using Microsoft.AspNet.OData.Builder;
using GL.Data.Models.EntityClass;
using Microsoft.Net.Http.Headers;
using Microsoft.AspNet.OData.Formatter;
using Newtonsoft.Json.Serialization;
using Microsoft.EntityFrameworkCore.Storage.ValueConversion.Internal;
using Newtonsoft.Json.Converters;

namespace GL.service
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc()
            .SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
            .AddJsonOptions(options =>
            {
                // Use camel case properties in the serializer and the spec (optional)
                options.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
                // Use string enums in the serializer and the spec (optional)
                options.SerializerSettings.Converters.Add(new StringEnumConverter());
            });

            // registers a Swagger v2.0 document with the name "v1" (default)
            services.AddSwaggerDocument(c => { 
            c.DocumentName = "V1";
                c.Title = "GL Controller";
            }); 
            services.AddOData();

        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();

            }
            else
            {

                app.UseHsts();
            }
            app.UseCors(b => b.AllowAnyHeader().AllowAnyMethod().AllowAnyOrigin().AllowCredentials());
            app.UseHttpsRedirection();
            app.UseAuthentication();

            app.UseOpenApi(); // Serves the registered OpenAPI/Swagger documents by default on 
            app.UseSwaggerUi3(); // Serves the Swagger UI 3 web ui to view the OpenAPI/Swagger 
            app.UseMvc(routeBuilder =>
            {
                routeBuilder.EnableDependencyInjection();
                routeBuilder.Expand().Select().Filter().Count().OrderBy();
            });
        }
    }
}

Please help to solve this problem.

Answer 1

Here is a workaround that you could fix API error(s) when NSwag UI loads.But OData isn't supported in Swashbuckle for AspNetCore and none of the OData endpoints will show in your NSwag UI.

services.AddOData();

services.AddMvcCore(options =>
{
    foreach (var outputFormatter in options.OutputFormatters.OfType<ODataOutputFormatter>().Where(_ => _.SupportedMediaTypes.Count == 0))
    {
        outputFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/prs.odatatestxx-odata"));
    }
    foreach (var inputFormatter in options.InputFormatters.OfType<ODataInputFormatter>().Where(_ => _.SupportedMediaTypes.Count == 0))
    {
        inputFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/prs.odatatestxx-odata"));
    }
});

Remember to place services.AddOData(); before the line services.AddMvcCore().

Refer to https://github.com/OData/WebApi/issues/1177