asp.net - DataTable to Json using jquery

Question

I'm trying to execute a web service which returns a DataTable with the following piece of code:

$.ajax({  
    type: "POST",  
    url: url,  
    data: data,   
    contentType: "application/json; charset=utf-8",  
    dataType: "json",  
    success: function(msg) {  
        //do things  
        }  
    }); 

If the webservice returns a class then it works so it has nothing to do with the input paramters etc. It only fails when the web method returns a datatable (the datatable only has 2 columns and 2 rows for the test I'm doing).

The WebService class is decorated with the [ScriptService] attribute so I thought that ASP.NET would automatically serialize the return value as JSON. It doesn't seem to work with datatable.

The only solution I've found was to return a string (a manually JSON serialized object) but it doesn't seem right to me to do it this way.
I'm using Visual Studio 2008 with .Net 3.5

Answer 1

In the end, I've decided to use the JavaScriptSerializer class to convert the DataTable into a JSON string. Unfortunately, this class doesn't work with a DataTable so I converted the DataTable into a list of dictionnaries and pass that list to the JavaScriptSerializer class. It takes only a few lines of code and it works fine.
Example in VB.net:

    Public Function GetJson(ByVal dt As DataTable) As String

        Dim serializer As System.Web.Script.Serialization.JavaScriptSerializer = New System.Web.Script.Serialization.JavaScriptSerializer()
        Dim rows As New List(Of Dictionary(Of String, Object))
        Dim row As Dictionary(Of String, Object)

        For Each dr As DataRow In dt.Rows
            row = New Dictionary(Of String, Object)
            For Each col As DataColumn In dt.Columns
                row.Add(col.ColumnName, dr(col))
            Next
            rows.Add(row)
        Next
        Return serializer.Serialize(rows)
    End Function