How do I turn a C# object into a JSON string in .NET?

Since we all love one-liners

... this one depends on the Newtonsoft NuGet package, which is popular and better than the default serializer.

Newtonsoft.Json.JsonConvert.SerializeObject(new {foo = "bar"})

Documentation: Serializing and Deserializing JSON

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Please Note

Microsoft recommends that you DO NOT USE JavaScriptSerializer

See the header of the documentation page:

For .NET Framework 4.7.2 and later versions, use the APIs in the System.Text.Json namespace for serialization and deserialization. For earlier versions of .NET Framework, use Newtonsoft.Json.

Original answer:

You could use the JavaScriptSerializer class (add reference to System.Web.Extensions):

using System.Web.Script.Serialization;

var json = new JavaScriptSerializer().Serialize(obj);

A full example:

using System;
using System.Web.Script.Serialization;

public class MyDate
{
    public int year;
    public int month;
    public int day;
}

public class Lad
{
    public string firstName;
    public string lastName;
    public MyDate dateOfBirth;
}

class Program
{
    static void Main()
    {
        var obj = new Lad
        {
            firstName = "Markoff",
            lastName = "Chaney",
            dateOfBirth = new MyDate
            {
                year = 1901,
                month = 4,
                day = 30
            }
        };
        var json = new JavaScriptSerializer().Serialize(obj);
        Console.WriteLine(json);
    }
}

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Use Json.Net library, you can download it from Nuget Packet Manager.

Serializing to Json String:

 var obj = new Lad
        {
            firstName = "Markoff",
            lastName = "Chaney",
            dateOfBirth = new MyDate
            {
                year = 1901,
                month = 4,
                day = 30
            }
        };

var jsonString = Newtonsoft.Json.JsonConvert.SerializeObject(obj);

Deserializing to Object:

var obj = Newtonsoft.Json.JsonConvert.DeserializeObject<Lad>(jsonString );

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Use the DataContractJsonSerializer class: MSDN1, MSDN2.

My example: HERE.

It can also safely deserialize objects from a JSON string, unlike JavaScriptSerializer. But personally I still prefer Json.NET.

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A new JSON serializer is available in the System.Text.Json namespace. It's included in the .NET Core 3.0 shared framework and is in a NuGet package for projects that target .NET Standard or .NET Framework or .NET Core 2.x.

Example code:

using System;
using System.Text.Json;

public class MyDate
{
    public int year { get; set; }
    public int month { get; set; }
    public int day { get; set; }
}

public class Lad
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public MyDate DateOfBirth { get; set; }
}

class Program
{
    static void Main()
    {
        var lad = new Lad
        {
            FirstName = "Markoff",
            LastName = "Chaney",
            DateOfBirth = new MyDate
            {
                year = 1901,
                month = 4,
                day = 30
            }
        };
        var json = JsonSerializer.Serialize(lad);
        Console.WriteLine(json);
    }
}

In this example the classes to be serialized have properties rather than fields; the System.Text.Json serializer currently doesn't serialize fields.

Documentation:

System.Text.Json overview

How to use System.Text.Json

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You can achieve this by using Newtonsoft.json. Install Newtonsoft.json from NuGet. And then:

using Newtonsoft.Json;

var jsonString = JsonConvert.SerializeObject(obj);

---

Wooou! Really better using a JSON framework :)

Here is my example using Json.NET (http://james.newtonking.com/json):

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

namespace com.blogspot.jeanjmichel.jsontest.model
{
    public class Contact
    {
        private Int64 id;
        private String name;
        List<Address> addresses;

        public Int64 Id
        {
            set { this.id = value; }
            get { return this.id; }
        }

        public String Name
        {
            set { this.name = value; }
            get { return this.name; }
        }

        public List<Address> Addresses
        {
            set { this.addresses = value; }
            get { return this.addresses; }
        }

        public String ToJSONRepresentation()
        {
            StringBuilder sb = new StringBuilder();
            JsonWriter jw = new JsonTextWriter(new StringWriter(sb));

            jw.Formatting = Formatting.Indented;
            jw.WriteStartObject();
            jw.WritePropertyName("id");
            jw.WriteValue(this.Id);
            jw.WritePropertyName("name");
            jw.WriteValue(this.Name);

            jw.WritePropertyName("addresses");
            jw.WriteStartArray();

            int i;
            i = 0;

            for (i = 0; i < addresses.Count; i++)
            {
                jw.WriteStartObject();
                jw.WritePropertyName("id");
                jw.WriteValue(addresses[i].Id);
                jw.WritePropertyName("streetAddress");
                jw.WriteValue(addresses[i].StreetAddress);
                jw.WritePropertyName("complement");
                jw.WriteValue(addresses[i].Complement);
                jw.WritePropertyName("city");
                jw.WriteValue(addresses[i].City);
                jw.WritePropertyName("province");
                jw.WriteValue(addresses[i].Province);
                jw.WritePropertyName("country");
                jw.WriteValue(addresses[i].Country);
                jw.WritePropertyName("postalCode");
                jw.WriteValue(addresses[i].PostalCode);
                jw.WriteEndObject();
            }

            jw.WriteEndArray();

            jw.WriteEndObject();

            return sb.ToString();
        }

        public Contact()
        {
        }

        public Contact(Int64 id, String personName, List<Address> addresses)
        {
            this.id = id;
            this.name = personName;
            this.addresses = addresses;
        }

        public Contact(String JSONRepresentation)
        {
            //To do
        }
    }
}

The test:

using System;
using System.Collections.Generic;
using com.blogspot.jeanjmichel.jsontest.model;

namespace com.blogspot.jeanjmichel.jsontest.main
{
    public class Program
    {
        static void Main(string[] args)
        {
            List<Address> addresses = new List<Address>();
            addresses.Add(new Address(1, "Rua Dr. Fernandes Coelho, 85", "15º andar", "São Paulo", "São Paulo", "Brazil", "05423040"));
            addresses.Add(new Address(2, "Avenida Senador Teotônio Vilela, 241", null, "São Paulo", "São Paulo", "Brazil", null));

            Contact contact = new Contact(1, "Ayrton Senna", addresses);

            Console.WriteLine(contact.ToJSONRepresentation());
            Console.ReadKey();
        }
    }
}

The result:

{
  "id": 1,
  "name": "Ayrton Senna",
  "addresses": [
    {
      "id": 1,
      "streetAddress": "Rua Dr. Fernandes Coelho, 85",
      "complement": "15º andar",
      "city": "São Paulo",
      "province": "São Paulo",
      "country": "Brazil",
      "postalCode": "05423040"
    },
    {
      "id": 2,
      "streetAddress": "Avenida Senador Teotônio Vilela, 241",
      "complement": null,
      "city": "São Paulo",
      "province": "São Paulo",
      "country": "Brazil",
      "postalCode": null
    }
  ]
}

Now I will implement the constructor method that will receives a JSON string and populates the class' fields.

---

If they are not very big, what's probably your case export it as JSON.

Also this makes it portable among all platforms.

using Newtonsoft.Json;

[TestMethod]
public void ExportJson()
{
    double[,] b = new double[,]
        {
            { 110,  120,  130,  140, 150 },
            {1110, 1120, 1130, 1140, 1150},
            {1000,    1,   5,     9, 1000},
            {1110,    2,   6,    10, 1110},
            {1220,    3,   7,    11, 1220},
            {1330,    4,   8,    12, 1330}
        };

    string jsonStr = JsonConvert.SerializeObject(b);

    Console.WriteLine(jsonStr);

    string path = "X:\\Programming\\workspaceEclipse\\PyTutorials\\src\\tensorflow_tutorials\\export.txt";

    File.WriteAllText(path, jsonStr);
}

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If you are in an ASP.NET MVC web controller it's as simple as:

string ladAsJson = Json(Lad);

Can't believe no one has mentioned this.

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I would vote for ServiceStack's JSON Serializer:

using ServiceStack;

string jsonString = new { FirstName = "James" }.ToJson();

It is also the fastest JSON serializer available for .NET: http://www.servicestack.net/benchmarks/

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Another solution using System.Text.Json (.NET Core 3.0+, .NET 5) where an object is self-sufficient and doesn't expose all possible fields:

A passing test:

using NUnit.Framework;

namespace Intech.UnitTests
{
    public class UserTests
    {
        [Test]
        public void ConvertsItselfToJson()
        {
            var userName = "John";
            var user = new User(userName);

            var actual = user.ToJson();

            Assert.AreEqual($"{{\"Name\":\"{userName}\"}}", actual);
        }
    }
}

An implementation:

using System.Text.Json;
using System.Collections.Generic;

namespace Intech
{
    public class User
    {
        private readonly string Name;

        public User(string name)
        {
            this.Name = name;
        }

        public string ToJson()
        {
            var params = new Dictionary<string, string>{{"Name", Name}};
            return JsonSerializer.Serialize(params);
        }
    }
}

---

It is as easy as this (it works for dynamic objects as well (type object)):

string json = new
System.Web.Script.Serialization.JavaScriptSerializer().Serialize(MYOBJECT);

---

In your Lad model class, add an override to the ToString() method that returns a JSON string version of your Lad object. Note: you will need to import System.Text.Json;

using System.Text.Json;

class MyDate
{
    int year, month, day;
}

class Lad
{
    public string firstName { get; set; };
    public string lastName { get; set; };
    public MyDate dateOfBirth { get; set; };
    public override string ToString() => JsonSerializer.Serialize<Lad>(this);
}

---

Here is another solution using Cinchoo ETL - an open source library

public class MyDate
{
    public int year { get; set; }
    public int month { get; set; }
    public int day { get; set; }
}

public class Lad
{
    public string firstName { get; set; }
    public string lastName { get; set; }
    public MyDate dateOfBirth { get; set; }
}

static void ToJsonString()
{
    var obj = new Lad
    {
        firstName = "Tom",
        lastName = "Smith",
        dateOfBirth = new MyDate
        {
            year = 1901,
            month = 4,
            day = 30
        }
    };
    var json = ChoJSONWriter.Serialize<Lad>(obj);

    Console.WriteLine(json);
}

Output:

{
  "firstName": "Tom",
  "lastName": "Smith",
  "dateOfBirth": {
    "year": 1901,
    "month": 4,
    "day": 30
  }
}

Disclaimer: I'm the author of this library.

---

Serializer

 public static void WriteToJsonFile<T>(string filePath, T objectToWrite, bool append = false) where T : new()
{
        var contentsToWriteToFile = JsonConvert.SerializeObject(objectToWrite, new JsonSerializerSettings
        {
            Formatting = Formatting.Indented,
        });
        using (var writer = new StreamWriter(filePath, append))
        {
            writer.Write(contentsToWriteToFile);
        }
}

Object

namespace MyConfig
{
    public class AppConfigurationSettings
    {
        public AppConfigurationSettings()
        {
            /* initialize the object if you want to output a new document
             * for use as a template or default settings possibly when 
             * an app is started.
             */
            if (AppSettings == null) { AppSettings=new AppSettings();}
        }

        public AppSettings AppSettings { get; set; }
    }

    public class AppSettings
    {
        public bool DebugMode { get; set; } = false;
    }
}

Implementation

var jsonObject = new AppConfigurationSettings();
WriteToJsonFile<AppConfigurationSettings>(file.FullName, jsonObject);

Output

{
  "AppSettings": {
    "DebugMode": false
  }
}

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