Question

I am a noob to ASP.NET/C#. I am trying to use a web service to return a JSON object from the database. I am getting an error in Firebug that I am creating a circular reference. The stack trace is in JSON format. When I view the web service directly in the browser, it is returning valid XML for some strange reason. Here is my web service.

[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)]
public DataSet Posts() {
    string connString = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["XXX"].ConnectionString;
    SqlConnection conn = new SqlConnection(connString);
    string sql = "SELECT * FROM Posts";
    SqlDataAdapter sda = new SqlDataAdapter(sql, conn);
    DataSet ds = new DataSet();
    sda.Fill(ds);
    return ds;
}

I’m new to C# so I don’t know if this is written correctly. What I want is a DataSet in JSON format. Am I doing this correctly? Here is the jQuery that is calling the web service.

<script>
    $(function () {
         $.ajax({
            type: "POST",
            url: "WebServices/MessageBoard.asmx/Posts",
            data: "{}",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function(data) { console.log(data) },
            failure: function (msg) {
                //alert(msg);
            }
        });

    });
</script>

Answer 1

The reason you’re getting XML is because the the DataSet serializes to XML. However, you can use JSON.NET to turn the XML into JSON. Here is an example:

using System;
using System.Collections.Generic;
using System.Data;

using Newtonsoft.Json;

class Program
{
    static void Main(string[] args)
    {
        var dataSet = new DataSet();
        var dataTable = new DataTable();
        for (int i = 0; i < 5; i++) { dataTable.Columns.Add(string.Format("Column{0}", i), typeof(string)); }
        for (int i = 0; i < 5; i++)
        {
            var vals = new List<object>();
            for (int j = 0; j < 5; j++) { vals.Add(string.Format("Value {0}", j)); }
            dataTable.LoadDataRow(vals.ToArray(), true);
        }

        dataSet.Tables.Add(dataTable);
        dataSet.AcceptChanges();

        Console.WriteLine(JsonConvert.SerializeObject(dataSet));
    }
}