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

In modern .NET projects, converting a C# object into a JSON string is straightforward. You can use:

  1. System.Text.Json (the recommended, built-in JSON library in .NET 5 and above)
  2. Newtonsoft.Json (a popular third-party library, often referred to as “Json.NET”)

Below, we’ll explore both.

1. Using System.Text.Json (Built-in)

Step 1: Import the Namespace

using System.Text.Json;

Step 2: Create Your C# Object

Let’s say you have a simple User class:

public class User
{
    public string Name { get; set; }
    public int Age { get; set; }
}

Step 3: Serialize to JSON

User user = new User { Name = "Alice", Age = 25 };
string jsonString = JsonSerializer.Serialize(user);
Console.WriteLine(jsonString);
// Output: {"Name":"Alice","Age":25}

Step 4: Pretty Print (Optional)

If you want a more readable JSON output:

var options = new JsonSerializerOptions
{
    WriteIndented = true
};

string prettyJson = JsonSerializer.Serialize(user, options);
Console.WriteLine(prettyJson);
/*
{
  "Name": "Alice",
  "Age": 25
}
*/

Key Advantages

  • Built-in: No extra NuGet packages needed.
  • Performance: Generally faster for most scenarios compared to older libraries.
  • Modern Features: Offers advanced options like ignoring null values, customizing property naming, etc.

2. Using Newtonsoft.Json (Json.NET)

Step 1: Install the Package

If you prefer Newtonsoft.Json (common in older projects), add the NuGet package:

dotnet add package Newtonsoft.Json

Step 2: Import the Namespace

using Newtonsoft.Json;

Step 3: Serialize Your Object

User user = new User { Name = "Bob", Age = 30 };
string jsonString = JsonConvert.SerializeObject(user);
Console.WriteLine(jsonString);
// Output: {"Name":"Bob","Age":30}

Step 4: Pretty Print (Optional)

string prettyJson = JsonConvert.SerializeObject(user, Formatting.Indented);
Console.WriteLine(prettyJson);
/*
{
  "Name": "Bob",
  "Age": 30
}
*/

When to Use Newtonsoft.Json?

  • Legacy or Existing Projects: Many established .NET applications use it.
  • Advanced Features: It has extensive support for custom converters, polymorphic types, etc.

Practical Tips

  1. Avoid Circular References: If your objects reference each other in a loop, serialization can fail unless you configure the serializer to handle it.
  2. Handle Missing/Extra Properties: Customize naming policies, ignore null values, or handle extra fields with your chosen library’s configuration options.
  3. Stay Up-to-Date: System.Text.Json has gained many features over recent .NET releases. Ensure you use the latest .NET version for the most robust functionality.

Level Up Your Coding Skills

If you’re looking to strengthen your overall coding abilities or prepare for software engineering interviews, here are a couple of courses from DesignGurus.io you might find helpful:

Final Thoughts

Converting a C# object to JSON in .NET is a snap with either System.Text.Json or Newtonsoft.Json. For most new projects, Microsoft recommends System.Text.Json for its performance and modern features. However, Newtonsoft.Json remains a solid choice for existing solutions or if you need some of its advanced capabilities.

By mastering these libraries and understanding how to serialize and deserialize objects, you’ll streamline data exchange between your .NET applications and the broader world of RESTful APIs, microservices, or front-end clients.

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