Ajax function being fired multiple times and returning error

Question

I'm trying to load information from the database into a table in asp.net using ajax call to WCF which gets the data from an entity table and loads them in the web page. I'm using the ajax call only once but the WCF is being loaded multiple times and it's always returning the right value but the complete function in Ajax is going to the error function The ajax call works fine with other WCF functions

WCF:

   #region Employees

    #region Get_Persons
    [OperationContract]
    [
    WebInvoke
    (
    Method = "POST",
    BodyStyle = WebMessageBodyStyle.WrappedRequest,
    ResponseFormat = WebMessageFormat.Json,
    RequestFormat = WebMessageFormat.Json
    )
    ]
    public Result_Get_Employees Get_Employees()
    {
        System.Diagnostics.Debug.WriteLine("wcf called"); //being printed multiple times
        #region Declaration And Initialization Section.
        string i_Ticket = string.Empty;
        Result_Get_Employees oResult_Get_Persons = new Result_Get_Employees();
        #endregion
        #region Body Section.
        FuelAppEntities entities = new FuelAppEntities();
            oResult_Get_Persons.My_Result = entities.tbl_User.ToList();
            #endregion
            #region Return Section
            System.Diagnostics.Debug.WriteLine("Result is: "+oResult_Get_Persons.My_Result.Count);//Returing the right value
            return oResult_Get_Persons;
        #endregion
    }
    #region Result_Get_Categories_List
    public partial class Result_Get_Employees : Action_Result
    {
        #region Properties.
        public List<tbl_User> My_Result { get; set; }
        #endregion
    }
    #endregion
    #endregion
    #endregion

    #region Action_Result
    public partial class Action_Result
    {
        #region Properties.
        public string ExceptionMsg { get; set; }
        #endregion
        #region Constructor
        public Action_Result()
        {
            #region Declaration And Initialization Section.
            #endregion
            #region Body Section.
            this.ExceptionMsg = string.Empty;
            #endregion
        }
        #endregion
    }
        #endregion

Javascript:

/* Members */
/* --------------------------------------------------------------- */
var _StartRow = 0;
var _Current_Page = 1;
var _Pages_Count = 0;
var _ChildWindow = "";
var js_Selected_News = null;
var _Person_Grid_Data = "";
var _Person_List = [];
var Params_Get_Person_By_Criteria_InList = new Object();
Params_Get_Person_By_Criteria_InList.data = ko.mapping.fromJS([]);

var _Params_Get_Person_By_Criteria_InList = ko.mapping.fromJS(Params_Get_Person_By_Criteria_InList);


$(document).ready
(
function () {
    console.log("ready");
    $("title", $(window.parent.document)).html('Persons');
    SetControlsProperties();
    setActiveNavigation(2, '');
}
);
/* --------------------------------------------------------------- */

/* SetControlsProperties */
/* --------------------------------------------------------------- */
function SetControlsProperties() {
    try {
        console.log("set control properties");
        /* ----------------- */
        ko.applyBindings(_Params_Get_Person_By_Criteria_InList, $("#news_page")[0]);
        /* ----------------- */
        Btn_Search_Click();
    }
    catch (e) {
        console.log("SetControlsProperties: " + e.message);
    }
}
/* --------------------------------------------------------------- */

/* Btn_Search_Click. */
/* --------------------------------------------------------------- */
function Btn_Search_Click() {
    try {
        console.log("btn search clicked");
        GetData();
    }
    catch (e) {
        console.log("Btn_Search_Click: " + e.message);
    }
}
/* --------------------------------------------------------------- */

/* GetData */
/* --------------------------------------------------------------- */
function GetData() {
    try {

        console.log("get data");
        _Params = ko.mapping.toJSON(_Params_Get_Person_By_Criteria_InList);
       // _Params = null;
        console.log("params: " + _Params);
        _Service_Method = "Get_Employees";
        var request = $.ajax({
        type: "POST",
        url: WCF.svc/Get_Employees,
        data: _Params,
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        async: true,
        success: function (msg) {
            console.log(msg.login);
            Get_Employees_Completed(msg);
        },
        error: function (msg) {
            console.log("fail: " + msg.responseText + msg.statusText + msg.status)
        }
    });

        /* ---------------- */
    }
    catch (e) {
        console.log("GetData: " + e.message);
    }
}
/* --------------------------------------------------------------- */
// Get_Person_By_Criteria_Adv
/* --------------------------------------------------------------- */
function Get_Employees_Completed(i_Input) {
    try {
        console.log(i_Input.message);
        Handle_Employees_Grid(i_Input);
    }
    catch (e) {
        console.log("Get_Employees_By_Criteria_Adv_Completed: " + e.message);
    }
}
/* --------------------------------------------------------------- */

//Handle_Person_Grid
/* --------------------------------------------------------------- */
function Handle_Employees_Grid(i_Input) {
    try {
        var i_Person_List = [];
        console.log("Length: " + i_Input.My_Result.length)
        for (var i = 0; i < i_Input.My_Result.length; i++) {
            console.log(i_Input.My_Result[i])
            i_Person_List.push("Persons: "+i_Input.My_Result[i]);
        }
        var oTable = $('#tbl_data').dataTable();
        oTable.fnDestroy();
         $('#tbl_data tbody').html("");
        _Person_List = i_Person_List;
        _Params_Get_Person_By_Criteria_InList.data([]);
        _Params_Get_Person_By_Criteria_InList.data(i_Person_List);
        Module.init();

    }
    catch (e) {
        console.log('Handle_Person_Grid :' + e.message);
    }
}
/* --------------------------------------------------------------- */

Answer 1

 public Result_Get_Employees Get_Employees() { System.Diagnostics.Debug.WriteLine("wcf called"); //being printed multiple times #region Declaration And Initialization Section. string i_Ticket = string.Empty; Result_Get_Employees oResult_Get_Persons = new Result_Get_Employees(); #endregion #region Body Section. FuelAppEntities entities = new FuelAppEntities(); return entities.tbl_User.ToList(); #endregion #region Return Section System.Diagnostics.Debug.WriteLine("Result is: "+oResult_Get_Persons.My_Result.Count);//Returing the right value return oResult_Get_Persons; #endregion } 

There might be something amiss in the code snippets. Generally speaking, we are supposed to return the list. Take the default WCF template as an example.
IService1.cs

[OperationContract]
        [WebGet(ResponseFormat = WebMessageFormat.Json, RequestFormat = WebMessageFormat.Json)]
        List<CompositeType> GetDataUsingDataContract();
[DataContract]
    public class CompositeType
    {
        bool boolValue = true;
        string stringValue = "Hello ";

        [DataMember]
        public bool BoolValue
        {
            get { return boolValue; }
            set { boolValue = value; }
        }

        [DataMember]
        public string StringValue
        {
            get { return stringValue; }
            set { stringValue = value; }
        }
}

Service1.cs

  public List<CompositeType> GetDataUsingDataContract()
    {
        List<CompositeType> lists = new List<CompositeType>()
        {
            new CompositeType()
            {
                StringValue="Hello",
                BoolValue=true
            },
            new CompositeType()
            {
               StringValue="busy",
               BoolValue=false
            },
           new CompositeType()
           {
               StringValue="World",
               BoolValue=true
           }
        };
        return lists;
    }

Knockoutjs binding.

  <script>
        var model = {
            composites: ko.observableArray()
        };

        function sendAjaxRequest(httpMethod, callback, url) {
            $.ajax("http://10.157.18.36:12000/service1.svc/getdatausingdatacontract", {
                type: httpMethod, success: callback
            });
        }

        function getAllItems() {
            sendAjaxRequest("GET", function (data) {
                model.composites.removeAll();
                for (var i = 0; i < data.length; i++) {
                    model.composites.push(data[i]);
                }
            });
        }

        $(document).ready(function () {
            getAllItems();
            ko.applyBindings(model);
        });
    </script>

Html.

<div class="panel-heading">List Composites</div>
    <div class="panel-body ">

        <table class="table table-striped table-condensed">
            <thead>
                <tr>
                    <th>
                        StringValue
                    </th>
                    <th>
                        BoolValue
                    </th>
                </tr>
            </thead>
            <tbody data-bind="foreach:model.composites">
                <tr>
                    <td data-bind="text:StringValue"></td>
                    <td data-bind="text:BoolValue"></td>

                </tr>
            </tbody>
        </table>
    </div>

Result. Feel free to let me know if there is anything I can help with.