System.Text.Json read-only property deserialization returns default value

[logcorner]

JsonSerializer.Deserialize returns null for readonly properties

public class WeatherForecast : Weather
   {
       private WeatherForecast()
       {
       }
       public WeatherForecast(DateTimeOffset date, string summary, int temperatureCelsius) : base(temperatureCelsius)
       {
           Date = date;
           Summary = summary;
       }

       public DateTimeOffset Date { get; }

       public string Summary { get; }
   }

   public class Weather
   {
       protected Weather()
       {
       }

       public Weather(int temperatureCelsius)
       {
           TemperatureCelsius = temperatureCelsius;
       }

       public int TemperatureCelsius { get; }
   }

the following call returns default for all properties

var weatherForecast = new WeatherForecast(DateTime.Now, "Hot", 25);
        string jsonString;
        jsonString = JsonSerializer.Serialize(weatherForecast);

        var DeserializeObject = JsonSerializer.Deserialize<WeatherForecast>(jsonString);

[Symbai]

You need [JsonInclude] attribute on your readonly property I believe. Only exists in .NET5 #34675 FYI: Might be necessary to explicit give them a private setter for JsonInclude to work, or this has been "fixed" as well. There were a few different approaches discussed during .NET5 development.

[layomia]

This code must have been run in .NET 3.x. This is fixed in .NET 5 - #33444. You can try out new JSON features in the .NET RC1 release - https://devblogs.microsoft.com/dotnet/announcing-net-5-0-rc-1/.

Since there is a single public constructor on the class, and the properties are public and deserialized via the constructor, JsonConstructorAttribute and JsonIncludeAttribute are not required to make this object deserializable as is.

Please let us know if you still face issues with this.

using System;
using System.Text.Json;

namespace quickcheck
{
    class Program
    {
        static void Main(string[] args)
        {
            var weatherForecast = new WeatherForecast(DateTime.Now, "Hot", 25);
            string jsonString;
            jsonString = JsonSerializer.Serialize(weatherForecast);

            var DeserializeObject = JsonSerializer.Deserialize<WeatherForecast>(jsonString);
            Console.WriteLine(DeserializeObject.Date);
            Console.WriteLine(DeserializeObject.Summary);
            Console.WriteLine(DeserializeObject.TemperatureCelsius);

            // 9 / 17 / 2020 9:27:24 PM - 07:00
            // Hot
            // 25
        }

        public class WeatherForecast : Weather
        {
            private WeatherForecast()
            {
            }
            public WeatherForecast(DateTimeOffset date, string summary, int temperatureCelsius) : base(temperatureCelsius)
            {
                Date = date;
                Summary = summary;
            }

            public DateTimeOffset Date { get; }

            public string Summary { get; }
        }

        public class Weather
        {
            protected Weather()
            {
            }

            public Weather(int temperatureCelsius)
            {
                TemperatureCelsius = temperatureCelsius;
            }

            public int TemperatureCelsius { get; }
        }
    }
}