👀 Views: 3 💬 Answers: 1 📅 Created: 2025-06-04

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

I tried several approaches but none seem to work. I've been working on a C# application using .NET 5 where I need to deserialize a JSON string into a polymorphic object structure. I created a custom `JsonConverter` to handle this, but I keep working with an `JsonException` when trying to deserialize the JSON. The relevant part of my code looks like this: ```csharp public class Animal { public string Name { get; set; } } public class Dog : Animal { public string Breed { get; set; } } public class Cat : Animal { public bool IsIndoor { get; set; } } public class AnimalConverter : JsonConverter<Animal> { public override Animal Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) { using (JsonDocument doc = JsonDocument.ParseValue(ref reader)) { var root = doc.RootElement; string animalType = root.GetProperty("Type").GetString(); if (animalType == "Dog") { return JsonSerializer.Deserialize<Dog>(root.GetRawText(), options); } else if (animalType == "Cat") { return JsonSerializer.Deserialize<Cat>(root.GetRawText(), options); } throw new JsonException($"Unknown animal type: {animalType}"); } } public override void Write(Utf8JsonWriter writer, Animal value, JsonSerializerOptions options) { // Serialization logic here } } ``` I am trying to deserialize this JSON: ```json { "Type": "Dog", "Name": "Rex", "Breed": "Golden Retriever" } ``` However, when I run my code, I receive a `JsonException: The JSON value could not be converted to System.String. Path: $.Type` behavior. I have ensured that the JSON structure matches my expectations, and I registered the converter like this: ```csharp var options = new JsonSerializerOptions(); options.Converters.Add(new AnimalConverter()); ``` When I debug, it seems that the reader is not correctly positioned to read the properties as I expect. I tried adjusting how I read the JSON and also the order of properties in my JSON, but nothing seems to resolve the scenario. How can I correctly implement this polymorphic deserialization for my object structure?