C# JSON Serialization

How it works

A JSON serializer understands JSON syntax, not the workshop’s business invariants. Deserialization can produce missing or default property values and can return null for a null document. Check the resulting object and its fields before treating it as an accepted booking. Pick an explicit property-name policy and decide how to handle extra fields, duplicate names and version changes for a real protocol. This fixture uses only built-in libraries and no external service.

Run it locally

Use the .NET 10 SDK with C# 14 in a separate console lab. Create an empty project once with dotnet new console --framework net10.0, then replace Program.cs with this complete source and add any supporting files shown. Keep only one lesson entry point in the project. C# does not currently run in Bhylu’s browser playground. Apache, PHP and MySQL are not needed.

dotnet build -p:LangVersion=14.0 -p:Nullable=enable -p:TreatWarningsAsErrors=true
dotnet run --no-build

Use the SDK’s project workflow; the review compiles against its matching reference assemblies and executes the results without external NuGet packages. File-writing examples belong in a private empty lab directory.

Download the complete C# source as Program.cs.

Example

using System;
using System.Text.Json;

internal static class Program
{
    private static void Main(string[] args)
    {
        const string json = "{\"Code\":\"W-17\",\"Places\":3}";
        BookingDto? booking = JsonSerializer.Deserialize<BookingDto>(json);
        if (booking is null || string.IsNullOrWhiteSpace(booking.Code) || booking.Places is < 1 or > 20)
            throw new InvalidOperationException("Invalid booking data");
        Console.WriteLine($"{booking.Code}: {booking.Places}");
        Console.WriteLine(JsonSerializer.Serialize(booking));
    }
}

internal sealed class BookingDto
{
    public string? Code { get; set; }
    public int Places { get; set; }
}

Expected result

W-17: 3
{"Code":"W-17","Places":3}

The nullable code property makes a missing code visible to analysis and validation. The chosen fixture deserializes successfully and serializes under the default property names. This does not prove every input is accepted safely; the advanced boundary tests supply malformed and invalid domain cases. Never manually concatenate untrusted text into JSON and hope quotes remain correct.