由于一些 JS 组件要求 JSON 格式是 PascalCase 格式，新版本 ASP.NET Core 3.0 中默认移除了 Newtonsoft.Json ，使用了微软自己实现的 System.Text.Json 来代替，可以修改继续使用 Newtonsoft.Json 来设置 PascalCase 格式属性名。

Install-Package Microsoft.AspNetCore.Mvc.NewtonsoftJson

           //返回 PascalCase 问题
            //services.AddMvc()
            //        .AddJsonOptions(option => option.JsonSerializerOptions.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver());

            services.AddControllersWithViews().AddNewtonsoftJson(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver()
            {
                NamingStrategy = new DefaultNamingStrategy()
            });

备注：使用 DefaultContractResolver 是 PascalCase 风格，使用 CamelCasePropertyNamesContractResolver 是 CamelCase 风格。

当然也可以使用默认的 System.Text.Json 来代替

services.AddControllersWithViews().AddJsonOptions(options => options.JsonSerializerOptions.PropertyNamingPolicy = null);

SignalR 问题

统一Hub 放在 UseEndpoints 下

SignalRAppBuilderExtensions.UseSignalR(IApplicationBuilder, Action<HubRouteBuilder>)”已过时:“This method is obsolete and will be removed in a future version. The recommended alternative is to use MapHub<THub> inside Microsoft.AspNetCore.Builder.UseEndpoints(...).

客户端迁移

SignalR JavaScript client has changed from @aspnet/signalr to @microsoft/signalr. 

REFER:
https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio#jsonnet-support

https://docs.microsoft.com/en-us/aspnet/core/signalr/javascript-client?view=aspnetcore-3.0
https://www.cnblogs.com/dudu/p/10776880.html
https://www.cnblogs.com/stulzq/p/11497624.html