What does the maxJsonLength property refer to?

Question

In a web forms project, I am loading a jqGrid using a SQL stored procedure where I return the data as json. During initial setup and testing, I was returning 85 rows of data. I then changed the parameters which caused 1,868 rows to be returned, except it was not displaying in the grid.

Upon debugging in Firebug, I saw the error "The length of the string exceeds the value set on the maxJsonLength property". I fixed it by setting the maxJsonLength="2147483647" in my webconfig as found in a popular Stackovrflow post.

So my question is what was the string that caused the error? Is it the length of the whole data record, or the length of the data in one of the columns returned?

I've seen examples of the jqGrid returning much more data. Thanks for any insight.

Update

I took Olegs advice and used Nuget to install Newtonsoft.Json in my project. I then made changes to my code to use it:

In the codebehind - .cs I have this:

using Newtonsoft.Json;

public partial class Default2 : System.Web.UI.Page {

[WebMethod]
public static string GetDataFromDB()

{
    DataSet ds = new DataSet();


    string con = System.Configuration.ConfigurationManager.ConnectionStrings["SQLCon"].ToString();
    SqlConnection SCon = new SqlConnection(con);
    SCon.Open();
    SqlCommand sqlCmd = new SqlCommand("dbo.usp_GetProjectDetails", SCon);
    sqlCmd.CommandType = CommandType.StoredProcedure;

    sqlCmd.Parameters.Add("@ProjNum", SqlDbType.Int).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@TrakIt", SqlDbType.VarChar, 255).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@Title", SqlDbType.VarChar, 255).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@Status", SqlDbType.VarChar, 255).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@Dept", SqlDbType.Int).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@AssignTo", SqlDbType.Int).Value = DBNull.Value;  //19;
    sqlCmd.Parameters.Add("@RecDate", SqlDbType.DateTime).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@CmpDate", SqlDbType.DateTime).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@EndDate", SqlDbType.DateTime).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@ExComp", SqlDbType.Int).Value = DBNull.Value;
    sqlCmd.Parameters.Add("@ExAcReq", SqlDbType.Int).Value = DBNull.Value;

    SqlDataAdapter da = new SqlDataAdapter(sqlCmd);
    da.Fill(ds);
    SCon.Close();

    return JsonConvert.SerializeObject(ds.Tables[0]);
}

The function in .aspx looks like this:

    <script type="text/javascript">
    $(document).ready(function () {
        $.ajax({
            type: "POST",
            contentType: "application/json",
            data: "{}",
            url: "Default2.aspx/GetDataFromDB",
            dataType: "json",
            success: function (data) {
                data = data.d;
                $("#list1").jqGrid({
                    datatype: "local",
                        colNames: ["Project #", "Trak-It #", "Priority", "Title", "Status", "Department", "Assigned To", "Resource", "Requestor"],
                        colModel: [
                                          { name: 'Project Number', index: 'Project Number', width: 80, key: true, formatter: 'showlink', formatoptions: { baseLinkUrl: 'Details.aspx', target: '_new' } },
                                          { name: 'Trak-It #', index: 'Trak-It #', width: 80 },
                                          { name: 'Priority', index: 'Priority', width: 80 },
                                          { name: 'Title', index: 'Title', width: 200 },
                                          { name: 'Status', index: 'Status', width: 80 },
                                          { name: 'Department', index: 'Department', width: 180 },
                                          { name: 'Assigned To', index: 'Assigned To', width: 100 },
                                          { name: 'Resource', index: 'Resource', width: 160 },
                                          { name: 'Requestor', index: 'Requestor', width: 140 }
                        ],
                        data: JSON.parse(data),
                        rowNum: 8,
                        rowList: [10, 20, 30],
                        pager: '#pager1',
                        caption: "Test Grid",
                        viewrecords: true,
                        ignoreCase: true,
                        async: true,
                        loadonce: true,
                        gridview: true,
                        width: 1000
                });
            }
        });
    });

</script>

And finally in Web.config, I commented out the maxjsonLength:

  <system.web.extensions>
<scripting>
  <webServices>
    <jsonSerialization maxJsonLength="2147483647">
    </jsonSerialization>
  </webServices>
</scripting>

But I still get the error = "Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property."

If I uncomment the web.config settings, it works just fine. If I leave it commented out and bring back less data, it works fine. What am I missing?

Answer 1

You mean probably System.Web.Script.Serialization.JavaScriptSerializer.MaxJsonLength property which need be increased globally if you use WebServices interface in the server code. The solution was described in the answer for example.

You ask about the background information of the problem. To tell the truth the main problem is that usage of very old WebService interface in ASP.NET applications. It was the first attempt by Microsoft, many years ago, to return XML or JSON data based on Content-Type header of HTTP request. It was implemented in .NET Framework 3.5. The web service should return object (not a string) which will be serialized by .NET framework to JSON string by usage of JavaScriptSerializer. Your code don't uses JavaScriptSerializer directly. Because you don't use JavaScriptSerializer directly, you can configure parameters of JavaScriptSerializer only in web.config.

In other words, you have to use MaxJsonLength settings of JavaScriptSerializer in web.config every time if the size of returned data could be larger as about 100k.

The restriction 100k for web method was relatively large 8 years ago (at 2007) at the time of publishing .NET Framework 3.5. Later Microsoft introduced WCF interface which made JSON serialization more quickly, and have not so small restriction. WCF is of case too old now too, but it allows still to make manual serialization using more performance version of JSON serializer (see the answer for example). After WCF Microsoft introduced ASP.NET MVC and then WebAPI. Now Microsoft works on ASP.NET 5 and MVC version 6, which combine MVC and WebAPI under one name MVC6. Starting with MVC2 (or MVC3) Microsoft stopped to develop own JSON serializer and suggested to use some other one. Microsoft use mostly Newtonsoft.Json (synonyme of Json.NET), which is not the most quick one, but relatively good and powefull.

I don't want to write too much too common things, but I would recommend you to go away from reto style of usage WebServices and go to some other interface which gives you more flefibility in choosing of JSON serializer. If you support some old code and can't use more modern technologies then I would recommend you to use ASHX handle, which are very old, but much more flexible as WebServices. I recommend you to look in the old answer, where I attached Visual Studio Project which used ASHX handle and return JSON data using Newtonsoft.Json (Json.NET). You can replace Newtonsoft.Json to any other JSON serializer class which you more like.