Error code 12031 in Ajax enabled wcf

From last couple of days I was trying to call a ajax enabled wcf service method with the help of jquery. But each and every time I am getting the error code 12031 returned by the service. I did googling for this error but I was unable to find the solution. After spending much time on R&D, I found the reason why I wa geeting this error.

In this article, I am going to share my experience with you so that you will be able to resolve this error in ajax enabled wcf service. I have the below service and code for calling wcf.

WCF Service

 namespace WCFBAL
{
 [DataContract]
 public class Employee
 {
 [DataMember]
 public int EmpID;
 [DataMember]
 public string Name;
 [DataMember]
 public int Salary;
 [DataMember]
 public DateTime JoiningDate;
 }
 [ServiceContract(Namespace = "")]
 [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
 public class WCFBALService
 {
 [WebInvoke(Method = "POST")]
 public Employee GetEmpInfo(int mEmpID)
 {
 try
 {
 //suppose you have a list of employee like as in the database
 List lst = new List() 
 { 
 new Employee { EmpID = 1, Name = "Deepak", Salary = 12000, JoiningDate = Convert.ToDateTime("11/05/2011") },
 new Employee { EmpID = 2, Name = "Mohan", Salary = 18000},
 new Employee { EmpID = 3, Name = "Mohan", JoiningDate = Convert.ToDateTime("06/10/2011") }
 };
 var q = lst.Where(m => m.EmpID == mEmpID).FirstOrDefault();
 Employee mobjEmp = new Employee();
 if (q != null)
 {
 mobjEmp.EmpID = q.EmpID;
 mobjEmp.Name = q.Name;
mobjEmp.Salary = q.Salary; // comment this line to expect same error 
 //The no error will be raised since "Salary" field is of int type and default value of int variable is "0", so zero value will be assigned to it. 
 mobjEmp.JoiningDate = q.JoiningDate; // comment this line and provide mEmpID=1 to raise error 
 //The error will be raised since "JoiningDate" field is not being serialized because this of DateTime and this has no default value and not assign any value to it.
 }
 return mobjEmp;
 }
 catch (Exception mex)
 {
 return null;
 }
 }
 }
} 

WCF Service Method Calling Code

 <script src="Scripts/jquery-1.4.1.min.js" type="text/javascript"></script> <script type="text/javascript">
 $('#btn').live('click', function () {
 // debugger;
 var value = $('#txtEmpID').val();
 if (value != '') {
 var strJSONFilterCriteria = '{"mEmpID":"' + value + '"}';
 $.ajax({ type: "POST", contentType: "application/json; charset=utf-8",
 url: '<%=ViewState["WCFBalUrl"]%>' + '/GetEmpInfo',
 data: strJSONFilterCriteria,
 dataType: "json",
 error: function (msg) {
 // debugger;
 alert('Service call failed: ' + msg.status + ' Type :' + msg.statusText);
 },
 success: function (msg) {
 //debugger;
 var str = "Emp ID:" + msg.d.EmpID + "\n";
 str += "Emp Name:" + msg.d.Name + "\n";
 str += "Emp Salary:" + msg.d.Salary + "\n";
 //str += "JoiningDate:" + new Date(parseInt(msg.d.JoiningDate.substr(6))) + "\n";
 alert(str);
 } }); }
 return false;
 });
 </script>
 <h2>
 WCF Error Code 12031
 </h2>
 <p>
 To learn more about Dot Net Tricks visit <a href="http://www.dotnet-tricks.com" title="Dot Net Tricks ">
 www.dotnet-tricks.com</a>.
 </p>
 <p>
 Enter Employee ID (1-3)
 </p>
 <p>
 <asp:TextBox ID="txtEmpID" runat="server" ClientIDMode="Static"></asp:TextBox>
  <asp:Button ID="btn" runat="server" Text="Get Info" ClientIDMode="Static" />
 </p> 

Summary

I hope you will enjoy this trick while programming with Ajax enabled WCF. I would like to have feedback from my blog readers. Your valuable feedback, question, or comments about this article are always welcome.