Startup.cs

public void ConfigureServices(IServiceCollection services) 
{ 
   services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DatabaseConnection"))); 
   services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2).AddJsonOptions(options => 
   { 
      options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore; 
   }); 
}