Unable to return List from AJAX call MVC ? Following one example mentioned

Question

I am trying to return a list from MVC controller. Value is returned easily when I am returning a hard code value. But when I am returning a list, it gives me an error. Here is my code ,

Ajax call,

function MyFunction() {
    alert($('#DDlSurvey').val());
    $.ajax({
        url: "@Url.Action("Index", "ConductSurvey")",
        data: { prefix: $('#DDlSurvey').val() },
        type: "POST",
        dataType: "json",
        success: function (data) {
             // loadData(data);
            alert("Success");
           // alert(data)
        },
        error: function (data){
            alert("Failed! Please try again.");
        }
    });
    //$('#YourLabelId').val('ReplaceWithThisValue');
}

and my method is,

[HttpPost]
public JsonResult Index(int prefix)
{

    List<SelectList> Questions = new List<SelectList>();
    List<Question> QuestionList = new List<Question>();
    List<string> ll = new List<string>();
    Question nn = new Question();
    SurveyAppEntities ObjectSur = new SurveyAppEntities();

    QuestionList = (from q in ObjectSur.Questions
                    join b in ObjectSur.SurveyQuestions on q.ID equals b.QuestionID
                    where b.SurveyID.Equals(prefix)
                    select q).ToList();
   //return Json("OK");
  return new JsonResult  {Data=QuestionList, JsonRequestBehavior=JsonRequestBehavior.AllowGet};
}

When I return OK i get it but when i try to return QuestionList It is not returning data and display Failed

I am also using one link for help in which every thing is as it is link is,

http://www.dotnetawesome.com/2014/05/how-to-retrieve-database-data-show-using-jquery-mvc-asp.html

Hopes for your suggestion

Can you show us the error in the console when you execute the AJAX call? — Ivan-San, Nov 29 '18 at 14:15
I am not familiar with fiddler but shows some error that is "Server Error in '/' Application. -------------------------------------------------------------------------------- A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.Question_BC320AE3E27C417948C0C84B1757D00A32BA9F8B496AD1AB2FBEB2D6D33E9DF7'" — john, Nov 29 '18 at 14:45
That's problem with the reference in your db. Try adding AsNoTracking() before your ToList() method. — Ivan-San, Nov 29 '18 at 18:17

score 1 · Accepted Answer · answered Nov 30 '18 at 02:45

A circular reference was detected indicates that EF generates proxy objects when generating query results which cannot be serialized using JsonResult. Assumed that SurveyAppEntities is your DbContext instance, then you need to do one of 2 options below:

1) Disable proxy creation

You need to set ProxyCreationEnabled property to false which prevent EF creating proxy objects which cannot be serialized:

[HttpPost]
public JsonResult Index(int prefix)
{

    List<SelectList> Questions = new List<SelectList>();
    List<Question> QuestionList = new List<Question>();
    List<string> ll = new List<string>();
    Question nn = new Question();
    SurveyAppEntities ObjectSur = new SurveyAppEntities();

    // this line is mandatory
    ObjectSur.Configuration.ProxyCreationEnabled = false;

    QuestionList = (from q in ObjectSur.Questions
                    join b in ObjectSur.SurveyQuestions on q.ID equals b.QuestionID
                    where b.SurveyID.Equals(prefix)
                    select q).ToList();

    return Json(QuestionList, JsonRequestBehavior.AllowGet);
}

2) Disable query result tracking

EF implements query result tracking with proxy objects which may be disabled by adding AsNoTracking() to each table entities:

[HttpPost]
public JsonResult Index(int prefix)
{

    List<SelectList> Questions = new List<SelectList>();
    List<Question> QuestionList = new List<Question>();
    List<string> ll = new List<string>();
    Question nn = new Question();
    SurveyAppEntities ObjectSur = new SurveyAppEntities();

    QuestionList = (from q in ObjectSur.Questions
                    join b in ObjectSur.SurveyQuestions on q.ID equals b.QuestionID
                    where b.SurveyID.Equals(prefix)
                    select q).AsNoTracking().ToList(); // prevents result tracking

    return Json(QuestionList, JsonRequestBehavior.AllowGet);
}

Note:

You may also try to return only required properties instead of entire ObjectSur.Questions object.

Related issue:

Circular reference detected exception while serializing object to JSON

got sicken tired of this issue your solution rocks ! – john Nov 30 '18 at 07:25 — john, Nov 30 '18 at 07:25

score 0 · Answer 2 · answered Nov 29 '18 at 11:43

0

Simply return list like below

return Json(QuestionList, JsonRequestBehavior.AllowGet);

answered Nov 29 '18 at 11:43

Muhammad Saqlain

2,112
4
33
48

Change JsonResult to ActionResult in Method Declaration – Muhammad Saqlain Nov 29 '18 at 12:42
Brother i tried but it is returning simple string in current case than why not List :( – john Nov 29 '18 at 13:55
You have to parse JSON at jquery end.. It will always return you a string. – Muhammad Saqlain Nov 29 '18 at 14:05
var json = $.parseJSON(data); – Muhammad Saqlain Nov 29 '18 at 14:08
means use in Success function ? – john Nov 29 '18 at 14:36

Unable to return List from AJAX call MVC ? Following one example mentioned

2 Answers2