How To Fix Circular Reference Error When Dealing W

问题:

This question is a part of my original post here Get Data Into Extjs GridPanel

Below is my Controller that reads data from sql db and then I am trying to encode the result as JSON and send the data back to my gridview.js

public JsonResult writeRecord()
//public string writeRecord()
    {

        Response.Write("Survey Completed!");
        SqlConnection conn = DBTools.GetDBConnection("ApplicationServices2");


        string sqlquery = "SELECT Q1, Q2, Q3, Q4, Improvements, Comments FROM myTable";
        SqlDataAdapter cmd = new SqlDataAdapter(sqlquery, conn);


        DataSet myData = new DataSet();
        cmd.Fill(myData, "myTable");

        conn.Open();
        conn.Close();

        return Json(myData, JsonRequestBehavior.AllowGet);
        //return myData.GetXml();

    } 

Here lies the problem, with the above code, I get my gridview table with no data when executing gridview.js, but if I directly access my controller's method like this

http://localhost:55099/GridView/writeRecord

I get this error,

A circular reference was detected while serializing an object of type 'System.Globalization.CultureInfo'. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.InvalidOperationException: A circular reference was detected while serializing an object of type 'System.Globalization.CultureInfo'.

Can someone please help..

回答1:

I use the following tool for serializing and deserializing JSON:

http://james.newtonking.com/pages/json-net.aspx

It's very easy to use and very lightweight.

While serializing we use this option:

JsonConvert.SerializeObject(myObject, Formatting.Indented, 
                            new JsonSerializerSettings { 
                                   ReferenceLoopHandling = ReferenceLoopHandling.Ignore 
                            })

It ignores circular references.

Also json.net from newtonking is extremely fast.

The other options is to use DTO's and map them via Automapper as mentioned by Diver.

Edit: I suspect your store is wrong:

var store = Ext.create('Ext.data.JsonStore', {      
        storeId: 'myData',
        reader: new Ext.data.JsonReader({
            root: 'myTable',
            fields: [{ name: 'Q1', type: 'int' },
                     { name: 'Q2', type: 'int' },
                     { name: 'Q3', type: 'int' },
                     { name: 'Q4', type: 'int' },
                     { name: 'Q5', type: 'int' },
                     { name: 'Improvements', type: 'string' },
                     { name: 'Comments', type: 'string'}]
        }),

        proxy: {
             type: 'json',
            url: 'GridView/writeRecord'
        }    
});  

回答2:

It's because something inside CultureInfo has a reference to itself (this type) and in process of converting to JSON it fails. To avoid this situation, you should use ViewModels (return to client only information that is needed). You can read more here http://blogs.msdn.com/b/dphill/archive/2009/01/31/the-viewmodel-pattern.aspx

In your situation you shoud create ViewModels for your data, convert your data to these data types and return them converted to JSON. For the purpose of converting from Model to ViewModel consider using AutoMapper http://automapper.codeplex.com/ or some similar tool.