👀 Views: 69 💬 Answers: 1 📅 Created: 2025-06-07

c# json serialization polymorphism system.text.json C#

I'm working on a personal project and I recently switched to I'm integrating two systems and I'm currently working on a C# application that involves serializing and deserializing polymorphic types to and from JSON using `System.Text.Json`..... I've defined a base class called `Animal` and two derived classes, `Dog` and `Cat`. The issue arises when I attempt to deserialize a JSON string that represents an array of these objects. Here’s the code for the classes: ```csharp public abstract class Animal { public string Name { get; set; } } public class Dog : Animal { public string Breed { get; set; } } public class Cat : Animal { public string Color { get; set; } } ``` When I attempt to deserialize the following JSON string: ```json [ { "Name": "Rex", "Breed": "Labrador" }, { "Name": "Whiskers", "Color": "Tabby" } ] ``` I use the following code: ```csharp var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver(), }; var animals = JsonSerializer.Deserialize<List<Animal>>(jsonString, options); ``` However, I encounter a `JsonException` with the message: "Unsupported JSON value type." It seems that `System.Text.Json` does not know how to handle the polymorphic nature of the `Animal` class. I've tried using `JsonConverter` to create a custom converter for `Animal`, but I keep running into various issues with the type resolution. I also attempted to implement a custom `JsonConverter` as shown below: ```csharp public class AnimalConverter : JsonConverter<Animal> { public override Animal Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) { using (JsonDocument doc = JsonDocument.ParseValue(ref reader)) { var element = doc.RootElement; if (element.TryGetProperty("Breed", out _)) { return JsonSerializer.Deserialize<Dog>(element.GetRawText(), options); } else if (element.TryGetProperty("Color", out _)) { return JsonSerializer.Deserialize<Cat>(element.GetRawText(), options); } } throw new JsonException(); } public override void Write(Utf8JsonWriter writer, Animal value, JsonSerializerOptions options) { JsonSerializer.Serialize(writer, value, value.GetType(), options); } } ``` Yet, I still receive the same exception. I've verified that I'm registering the converter correctly in the options. Any insights on how to effectively handle polymorphic JSON serialization and deserialization using `System.Text.Json` would be greatly appreciated. I'm working in a macOS environment. This issue appeared after updating to C# stable. Any examples would be super helpful. What are your experiences with this? I'm working in a Ubuntu 20.04 environment. Thanks, I really appreciate it!