System.Text.Json: How do I serialize an object to be a nested subobject with a key?

Question

I have an object of the following class that I want to serialize:

[Serializable]
public class BuildInfo
{
    public DateTime BuildDate { get; set; }

    public string BuildVersion { get; set; }
}

I wrote the following method to serialize any objects:

...
public static string JsonSerialize<TValue>(TValue value)
{
    var options = new JsonSerializerOptions
    {

        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        WriteIndented = true
    };

    return JsonSerializer.Serialize(value, options);
}
...

I got the following output (example):

{
    "buildDate": "2021-04-22T17:29:59.1611109+03:00",
    "buildVersion": "1.0.1"
}

I want to get output like this:

{
    "buildInfo": {
        "buildDate": "2021-04-22T17:29:59.1611109+03:00",
        "buildVersion": "1.0.1"
    }
}

How can I do it?

Answer 1

Taking all the answers and comments into account, I got the following code:

public static class JsonUtilities
{
    public static string JsonSerializeTopAsNested<TValue>(TValue? value, JsonSerializerOptions? options = null)
    {
        return JsonSerializer.Serialize(ToSerializableObject(value, options), options);
    }

    public static async Task<string> JsonSerializeTopAsNestedAsync<TValue>(TValue? value,
        JsonSerializerOptions? options = null, CancellationToken cancellationToken = default)
    {
        await using var stream = new MemoryStream();
        await JsonSerializer.SerializeAsync(stream, ToSerializableObject(value, options), options,
            cancellationToken);

        return Encoding.UTF8.GetString(stream.ToArray());
    }

    public static TValue? JsonDeserializeTopAsNested<TValue>(string json, JsonSerializerOptions? options = null)
    {
        var serializableObject = JsonSerializer.Deserialize<Dictionary<string, TValue?>>(json, options);

        return FromSerializableObject(serializableObject, options);
    }

    public static async Task<TValue?> JsonDeserializeTopAsNestedAsync<TValue>(string json,
        JsonSerializerOptions? options = null, CancellationToken cancellationToken = default)
    {
        await using var stream = new MemoryStream(Encoding.UTF8.GetBytes(json));
        var serializableObject = await JsonSerializer.DeserializeAsync<Dictionary<string, TValue?>>(stream, options,
            cancellationToken);

        return FromSerializableObject(serializableObject, options);
    }

    private static Dictionary<string, TValue?> ToSerializableObject<TValue>(TValue? propertyValue,
        JsonSerializerOptions? options)
    {
        var propertyName = GetPropertyName<TValue>(options);

        return propertyValue == null && options is {IgnoreNullValues: true}
            ? new Dictionary<string, TValue?>()
            : new Dictionary<string, TValue?> {[propertyName] = propertyValue};
    }

    private static TValue? FromSerializableObject<TValue>(IReadOnlyDictionary<string, TValue?>? serializableObject,
        JsonSerializerOptions? options)
    {
        var propertyName = GetPropertyName<TValue>(options);

        return serializableObject != null && serializableObject.ContainsKey(propertyName)
            ? serializableObject[propertyName]
            : default;
    }

    private static string GetPropertyName<TValue>(JsonSerializerOptions? options)
    {
        var propertyName = typeof(TValue).Name;
        return options?.PropertyNamingPolicy?.ConvertName(propertyName) ?? propertyName;
    }
}

I would appreciate additional comments and bugs found.