using System;

using System.Collections.Generic;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var jsonString = "{\"Date\": \"2019-08-01T00:00:00-07:00\",  \"TemperatureCelsius\": 25,  \"Summary\": \"Hot\",  \"DatesAvailable\": [    \"2019-08-01T00:00:00-07:00\",    \"2019-08-02T00:00:00-07:00\"  ],  \"SummaryWords\":    {\"Temprature\": {\"Type\": \"Cool\"}}  }";

        var weatherForecast = JsonSerializer.Deserialize<WeatherForecastWithExtensionData>(jsonString);

        Console.WriteLine(weatherForecast.ExtensionData["SummaryWords"].GetPropertyExtension("Temprature")?.GetPropertyExtension("Type"));

        Console.WriteLine("Hello World");

    }

}

​

public static class JsonElementExtenstion

{

    public static JsonElement? GetPropertyExtension(this JsonElement jsonElement, string propertyName)

    {

        if (jsonElement.TryGetProperty(propertyName, out JsonElement returnElement))

        {

            return returnElement;

        }

        return null;

    }

}

​

public class WeatherForecastWithExtensionData

{

    public DateTimeOffset Date { get; set; }

    public int TemperatureCelsius { get; set; }

    public string Summary { get; set; }

    [JsonExtensionData]

    public Dictionary<string, JsonElement> ExtensionData { get; set; }

}