c# - 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 convert it to a class. EG:

var str = ""; // some json string
var jObj = JObject.Parse(str);
var myClass = jObj["SomeProperty"].ToObject<SomeClass>();

How would we be able to do this with .NET Core 3's new System.Text.Json

var str = ""; // some json string
var jDoc = JsonDocument.Parse(str);
var myClass = jDoc.RootElement.GetProperty("SomeProperty"). <-- now what??

Initially I was thinking I'd just convert the JsonElement that is returned in jDoc.RootElement.GetPRoperty("SomeProperty") to a string and then deserialize that string. But I feel that might not be the most efficient method, and I can't really find documentation on doing it another way.

Answer 1

I came across the same issue, so I wrote some extension methods which work fine for now. It would be nice if they provided this as built in to avoid the additional allocation to a string.

public static T ToObject<T>(this JsonElement element)
{
    var json = element.GetRawText();
    return JsonSerializer.Deserialize<T>(json);
}
public static T ToObject<T>(this JsonDocument document)
{
    var json = document.RootElement.GetRawText();
    return JsonSerializer.Deserialize<T>(json);
}

Then use as follows:

jDoc.RootElement.GetProperty("SomeProperty").ToObject<SomeClass>();