How to Append a list Into Existing JSON File

Hey, if you're getting a NullReferenceException when trying to add the courses to data.Courses, it means that the Courses property is null. You need to initialize it with a new instance of List before adding items to it.

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

class Program
{
    static void Main()
    {
        string json = "ExistingJsonData";
        var data = JsonConvert.DeserializeObject(json);
        var courses = new List
        {
            new Course { Name = "English" },
            new Course { Name = "Maths" }
        };

        // Initialize the Courses property if it's null
        if (data.Courses == null)
        {
            data.Courses = new List();
        }

        data.Courses.AddRange(courses);
        string updatedJson = JsonConvert.SerializeObject(data, Formatting.Indented);
        Console.WriteLine("Courses appended to the JSON file successfully.");
    }
}

class Data
{
    public int UniqueID { get; set; }
    public string Datetime { get; set; }
    public string User { get; set; }
    public List Courses { get; set; }
}

class Course
{
    public string Name { get; set; }
}

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

class Program
{
    static void Main()
    {
        string json = "ExistingJsonData";
        var data = JsonConvert.DeserializeObject(json);

        // Initialize the Courses list if it's null
        data.Courses = data.Courses ?? new List();

        var courses = new List
        {
            new Course { Name = "English" },
            new Course { Name = "Maths" }
        };
        data.Courses.AddRange(courses);
        string updatedJson = JsonConvert.SerializeObject(data, Formatting.Indented);
        Console.WriteLine("List data appended to the JSON data successfully.");
    }
}

class Data
{
    public int UniqueID { get; set; }
    public string Datetime { get; set; }
    public string User { get; set; }
    public List Courses { get; set; }

    // Constructor to initialize the Courses list
    public Data()
    {
        Courses = new List();
    }
}

class Course
{
    public string Name { get; set; }
}

Hi!!

var courses = new List { new Course { Name = "English" }, new Course { Name = "Maths" } };  If i want to add the courses through dynamically how should i append into courses. Trying to Append but it replace the old content but not new course is not appending

Hi Amit

 data.Courses.AddRange(courses); 

While adding am getting System.NullReferenceException: 'Object reference not set to an instance of an object.' but when i debug having data .

Check this:

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

class Program
{
    static void Main()
    {
        string json = "ExistingJsonData";
        var data = JsonConvert.DeserializeObject(json);
        var courses = new List
        {
            new Course { Name = "English" },
            new Course { Name = "Maths" }
        };
        data.Courses.AddRange(courses);
        string updatedJson = JsonConvert.SerializeObject(data, Formatting.Indented);
        Console.WriteLine("List data appended to the JSON data successfully.");
    }
}

class Data
{
    public int UniqueID { get; set; }
    public string Datetime { get; set; }
    public string User { get; set; }
    public List Courses { get; set; }
}

class Course
{
    public string Name { get; set; }
}