System.Text.Json.JsonElement ToObject workaround

Question

I want to know the equivalent of the ToObject<>() method in Json.NET for System.Text.Json.

Using Json.NET you can use any JToken and

Answer 1

There is an open enhancement about this, currently targeted for Future:

• We should be able serialize and serialize from DOM #31274.

In the interim you may get better performance by writing to an intermediate byte buffer rather than to a string, since both JsonDocument and Utf8JsonReader work directly with byte spans rather than strings or char spans. As stated in the docs:

Serializing to UTF-8 is about 5-10% faster than using the string-based methods. The difference is because the bytes (as UTF-8) don't need to be converted to strings (UTF-16).

public static partial class JsonExtensions
{
    public static T ToObject(this JsonElement element, JsonSerializerOptions options = null)
    {
        var bufferWriter = new ArrayBufferWriter();
        using (var writer = new Utf8JsonWriter(bufferWriter))
            element.WriteTo(writer);
        return JsonSerializer.Deserialize(bufferWriter.WrittenSpan, options);
    }

    public static T ToObject(this JsonDocument document, JsonSerializerOptions options = null)
    {
        if (document == null)
            throw new ArgumentNullException(nameof(document));
        return document.RootElement.ToObject(options);
    }       
}

Demo fiddle here.