Working with JSON in C# (Json.NET)

I’ve put together some usage examples for Json.NET in C#. The reason being that I keep forgetting them… I plan to keep updating this.

Of course, the official docs are the best resource.

Getting GET parameters

string course_no = Request["course_no"];
string haksu_no = Request["haksu_no"];

Getting a POST request

using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

string rawRequest = Request.Form[0];
JObject applyJObj = JObject.Parse(rawRequest);

Example JSON

// applyJObj	
{  
  "counselHopeTime": [
    {
      "key": 1,
      "date": "20180814",
      "time": "03"
    },
    {
      "key": 1533569780046,
      "date": "20180807",
      "time": "05"
    }
  ],
  "subject": {
    "life": [],
    "etc": ""
  },
  "problem": "this is the problem",
  "goal": "change"
}

Getting an Object value

string goal = applyData["goal"].ToString();

Getting an Object value inside an Object

string etc = applyData["subject"]["etc"].ToString();

Joining the values inside an Array with ‘, ‘ into a string

string life = string.Join(", ", JsonConvert.DeserializeObject<List<string>>(applyData["subject"]["life"].ToString()).ToArray());

Iterating over properties and handling the Array case

foreach (JProperty property in applyJObj.Properties())
{
    if (property.Value.Type == JTokenType.Array) // when it's an Array
    {
        List<string> listInProperty = JsonConvert.DeserializeObject<List<string>> (property.Value.ToString());
        property.Value = string.Join(",", listInProperty.ToArray());
    }
}

Building an Array of 10 elements with foreach

string[] hopeDateArr = {"0000000000", "0000000000", "0000000000", "0000000000", "0000000000", "0000000000", "0000000000", "0000000000", "0000000000", "0000000000"};
            
int hopeDateCnt = 0;
foreach(JObject hopeTime in applyData["counselHopeTime"])
{
    string dt = hopeTime["date"].ToString();
    hopeDateArr[hopeDateCnt] = dt;
    hopeDateCnt++;
}

Building JSON

Building it with a Dictionary

string uploadedUrl = "http://whereTheFileWas.com/uploaded/what.jpg"
Dictionary<string, string> location = new Dictionary<string, string>
{
    {"location", uploadedUrl}
};
string json = JsonConvert.SerializeObject(location, Formatting.Indented);

Reducing unnecessary data transfer

Converting a single-column DataTable into an Array

The example DataTable has only one column, APPLY_DATE. Converting it directly to json results in a lot of unnecessary data transfer. To send only the plain string values, let’s convert it to an ArrayList before sending.

/* before
[
  {
    "APPLY_DATE": "20190311"
  },
  {
    "APPLY_DATE": "20190313"
  },
  {
    "APPLY_DATE": "20190314"
  }
]
*/
DataTable dt = new DataTable();
DataColumn column = new DataColumn();
column.DataType = System.Type.GetType("System.String");
column.ColumnName = "APPLY_DATE";
dt.Columns.Add(column);
DataRow row1 = dt.NewRow();
row1["APPLY_DATE"] = "20190311";
dt.Rows.Add(row1);
DataRow row2 = dt.NewRow();
row2["APPLY_DATE"] = "20190313";
dt.Rows.Add(row2);
DataRow row3 = dt.NewRow();
row3["APPLY_DATE"] = "20190314";
dt.Rows.Add(row3);

string json = JsonConvert.SerializeObject(dt, Formatting.Indented);

/* after
[
  "20190311",
  "20190313",
  "20190314"
]
*/
ArrayList converted = new ArrayList(dt.Rows.Count);
foreach (DataRow row in dt.Rows)
{
    converted.Add(row.ItemArray[0].ToString());
}
string json = JsonConvert.SerializeObject(converted, Formatting.Indented);