1、需要安装两个包

Newtonsoft.Json

Microsoft.AspNetCore.Mvc.NewtonsoftJson

2、 Startup 类中的 ConfigureServices 方法插入如下代码

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddControllers().AddNewtonsoftJson(options =>
            {
                options.SerializerSettings.ContractResolver = new 
      DefaultContractResolver();
            });
  }