Startup.cs

using BookHub.DataProvider;
using BookHub.Repositories;
using Microsoft.EntityFrameworkCore;
using Microsoft.OpenApi.Models;
using System.Text.Json.Serialization;

namespace BookHub
{
    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.AddControllers()
            .AddJsonOptions(options =>
            {
                options.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.Preserve;
            });

            services.AddDbContext<BookContext>(options =>
                options.UseInMemoryDatabase(databaseName: "BooksDatabase"));
            services.AddTransient(typeof(IRepository<>), typeof(Repository<>));

            // Enable CORS
            services.AddCors(options =>
            {
                options.AddPolicy("AllowAllOrigins",
                    builder => builder.AllowAnyOrigin().AllowAnyHeader().AllowAnyMethod());
            });

            // Register the Swagger generator and define a Swagger document for BookHub API
            services.AddSwaggerGen(c =>
            {
                c.SwaggerDoc("v1", new OpenApiInfo { Title = "BookHub API", Version = "v1" });
            });
        }

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

            app.UseSwagger();
            app.UseSwaggerUI();

            app.UseHttpsRedirection();

            app.UseRouting();

            // Enable CORS
            app.UseCors("AllowAllOrigins");

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });

            app.Run(async (context) => await context.Response.WriteAsync("There is no page with a default path, so you need to open the /swagger path!"));
        }
    }
}