In the mvc EF framework, an error occurs when the foreign key object is serialized when the object is serialized. A circular reference is detected when an object of type XX is serialized

Newtonsoft.Json.dll or enter Newtonsoft or json.net online via ->Tools->Library Package Management Tools->NuGet Management Packages->

Newtonsoft.Json is ok:

 

context.Response.ContentType = "text/plain";
BooksService service = new BooksService();
List<Books> list=service.GetAll().Take(5).ToList();
JsonSerializerSettings setting = new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore
};

strintret = JsonConvert.SerializeObject(list, setting);
context.Response.Write(ret);