Circular reference was detected while serializing an object of type

Question

I am trying to fetch company data based on company id through ajax and fill the related textboxes with the received data. Company id is selected through ajax autocomplete. The code was working fine two days back and suddenly it started generating an error for only first two entries of autocomplete and for rest it is working fine. Can anyone point out the mistake in this. Thank you.

Error Details: "Message":"A circular reference was detected while serializing an object of type \u0027System.Data.Entity.DynamicProxies.Company_81625299B5B4D7A3375D55E48BE84921728B8D48335366DF8CA6844A8D10FF5D\u0027.","StackTrace":" at System.Web.Script.Serialization.JavaScriptSerializer.SerializeValueInternal(Object o, StringBuilder sb, Int32 depth, Hashtable objectsInUse, SerializationFormat serializationFormat, MemberInfo currentMember)\r\n.

Below is my code:

function setCompanyData(pageurl, txtboxid, txtResultid) {
var temp = true;
var searchTbox = $jq14("[id$=" + txtboxid + "]");
var resultTbox = $jq14("[id$=" + txtResultid + "]");

searchTbox.autocomplete({
    source: function (request, response) {
        $jq14.ajax({
            url: pageurl,
            data: "{ 'SearchText': '" + request.term + "'}",
            dataType: "json",
            type: "POST",
            contentType: "application/json; charset=utf-8",
            success: function (data) {
                response($.map(data.d, function (item) {

                    return {
                        label: item.split('*')[0],
                        val: item.split('*')[1]
                    }
                }))
            },
            error: function (response) {
                alert(response.responseText);
            },
            failure: function (response) {
                alert(response.responseText);
            }
        });
    },
    autoSelect: true,
    autoFocus: true,
    select: function (e, i) {
        // e.preventDefault();
        searchTbox.val(i.item.label);
        resultTbox.val(i.item.val).trigger('change');
        temp = true;
        // return false;
    },
    change: function (e, i) {

        var cId = resultTbox.val();
        if (isEmptyOrSpaces(cId)) {
            // error 
            cId = 0;
            searchTbox.val("").trigger('');
        }
        if (isEmptyOrSpaces(searchTbox.val())) {
            // error 
            cId = 0;
            resultTbox.val("").trigger('change');
        }
        getCompanyDetails(cId);
    },
    minLength: 0
}).focus(function () {
    if (temp) {
        $jq14(this).autocomplete("search", "");
        temp = false;
    }
});

searchTbox.autocomplete("widget").addClass("fixedHeight");}


function getCompanyDetails(cid) {
 $jq14.ajax({
     url: "/sw/adm/update-delete-company.aspx/GetCompanyData",
     data: "{ 'cId': '" + cid + "'}",
     dataType: "json",
     type: "POST",
     contentType: "application/json; charset=utf-8",
     beforeSend: function () {
         $('#loader').show();
     },
     complete: function () {
         $('#loader').hide();
         $("#messageBox").hide().slideDown();
         setTimeout(function () {
             $("#messageBox").fadeOut(); 
         }, 5000);

     },
     success: function (result) {
         $jq14('#cphMainLeft_txtAddress').val(result.d.CompanyAddress);
         $jq14('#cphMainLeft_txtCountry').val(result.d.CompanyCountry);
         $jq14('#cphMainLeft_txtCity').val(result.d.CompanyCity);
         $jq14('#cphMainLeft_txtNewCompanyName').val(result.d.CompanyName);
         $jq14('#cphMainLeft_txtEmail').val(result.d.CompanyEmail);
         $jq14('#cphMainLeft_txtPanNo').val(result.d.CompanyPAN);
         $jq14('#cphMainLeft_txtTinNo').val(result.d.CompanyTIN);
         $jq14('#cphMainLeft_txtPhone').val(result.d.CompanyPhone);
         $jq14('#cphMainLeft_txtPincode').val(result.d.CompanyPincode);
         $jq14('#cphMainLeft_hfTxtCountry').val(result.d.CompanyCountry);
         $jq14("#cphMainLeft_ddlCompanyType").val(result.d.CompanyType);
     },
     error: function (response) {
         alert(response.responseText);
     },
     failure: function (response) {
         alert(response.responseText);
     }
 });
}

C# Webmethod goes like:

    [WebMethod]
    public static Company GetCompanyData(int cId)
    {
        Entities db = new Entities();

        var companyRecord = (from cmp in db.Companies
                                 where cmp.CompanyId == cId
                                 select cmp).SingleOrDefault();

            if (companyRecord != null)
                return companyRecord;
            else
                return new Company();
    }

Answer 1

Thank you Ashokkumar M. Prajapati for providing the hint.

Instead of returning Company object from [WebMethod], I have converted the company object to Json string in code behind and returned it.

Here is my WebMethod:

[WebMethod]
public static string GetCompanyData(int cId)
{
    Entities db = new Entities();

    var companyRecord = (from cmp in db.Companies
                             where cmp.CompanyId == cId
                             select cmp).SingleOrDefault();


        if (companyRecord == null)
            companyRecord = new Company();

        string s = string.Empty;
        s = JsonConvert.SerializeObject(companyRecord,
                       new JsonSerializerSettings
                       {
                           ReferenceLoopHandling = ReferenceLoopHandling.Ignore
                       });
        return s;

}

Then I updated the success method of getCompanyDetails(cid) to:

    success: function (result) {
         res = JSON.parse(result.d);
         $jq14('#cphMainLeft_txtAddress').val(res['CompanyAddress']);
         $jq14('#cphMainLeft_txtCountry').val(res['CompanyCountry']);
         $jq14('#cphMainLeft_txtCity').val(res['CompanyCity']);
         $jq14('#cphMainLeft_txtNewCompanyName').val(res['CompanyName']);
         $jq14('#cphMainLeft_txtEmail').val(res['CompanyEmail']);
         $jq14('#cphMainLeft_txtPanNo').val(res['CompanyPAN']);
         $jq14('#cphMainLeft_txtTinNo').val(res['CompanyTIN']);
         $jq14('#cphMainLeft_txtPhone').val(res['CompanyPhone']);
         $jq14('#cphMainLeft_txtPincode').val(res['CompanyPincode']);
         $jq14('#cphMainLeft_hfTxtCountry').val(res['CompanyCountry']);
         $jq14("#cphMainLeft_ddlCompanyType").val(res['CompanyType']);
     }

and it worked wonderfully. Thanks again.