Ajax-Call to get JSON Result from Controller (returning IList) in Asp.Net MVC always errors

Question

I am trying to make an AJAX-Call (Javascript) in order to get a IList created in a Controller-method.

index.js:

function getList() {
    $.ajax({
        url: myUrl, 
        type: "GET",
        dataType: "json",    
        success: function (response) {
            if (response) {
                //do sth
            }
        },
        error: function (response) {   
            alert("error");  //always error
            console.log(response); //object with just default functions
        }
   });

}

MyController.cs:

 public IList<SomeItem> loadList()
 {
        var items = db.SomeItemSet.Include(item => item.Sth).ToList();

        IList<SomeItem> resultList = new List<SomeItem>();

        for (int i = 0; i < items.Count(); i++)
        {
            //if(condition)
               resultList.Add(items[i]);                  
        }
        return resultList;
}

public JsonResult loadListJson()
{
    return Json(new { response = loadList() }, JsonRequestBehavior.AllowGet);
}

A breakpoint in the Controllermethod shows me that it is executed. The list is not null.

I also tried to declare the method as Action Result (return json without jsonreqbehaviour) and doing type: POST in the ajax-Call. What do you think could fail here?

The network debugging panel shows the code

302:found

(but not 200:OK) when trying to loadListJson.

Exception:

System.InvalidOperationException: A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.SomeItem_9D..'. at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)
at ...

Answer 1

It seems that there are circular references in your object structure .It is not supported by the JSON serializer. Try Select() method. Something like below.

 var items = db.SomeItemSet.Include(item => item.Sth).Select(s=> new SomeItemDto{
 // which properties you need
}).ToList();

Answer 2

I used Newtonsoft.Json.JsonConvert to convert my list !

index.js:

function getList() {
    $.ajax({
        url: myUrl, 
        type: "POST", //
        dataType: "json",    
    success: function (list) {
        if (list) {
            //do sth 
        }
    },
    error: function (response) { //do sth }
   });
}

MyController.cs:

 public ActionResult loadListJson()
        {
            return Content(Newtonsoft.Json.JsonConvert.SerializeObject(loadList()), "application/json");
        }