How to Handle JSON Deserialization implementing Polymorphic Types in .NET 6 using System.Text.Json?
I'm dealing with I've searched everywhere and can't find a clear answer... I'm working with a scenario with JSON deserialization in .NET 6 using the `System.Text.Json` library when working with polymorphic types. My scenario involves a base class `Animal` and derived classes `Dog` and `Cat`. The JSON being deserialized has a type discriminator field, but I keep getting an `InvalidOperationException` stating that the converter want to handle the provided type. Here’s my base structure: ```csharp public abstract 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; } } ``` The JSON looks something like this: ```json [ { "Type": "Dog", "Name": "Rex", "Breed": "Labrador" }, { "Type": "Cat", "Name": "Whiskers", "IsIndoor": true } ] ``` I’ve tried creating a custom converter for `Animal`, but it seems to be bypassed. Here’s the converter I attempted: ```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 jsonObject = doc.RootElement; string type = jsonObject.GetProperty("Type").GetString(); if (type == "Dog") return JsonSerializer.Deserialize<Dog>(jsonObject.GetRawText(), options); else if (type == "Cat") return JsonSerializer.Deserialize<Cat>(jsonObject.GetRawText(), options); } throw new JsonException(); } public override void Write(Utf8JsonWriter writer, Animal value, JsonSerializerOptions options) { JsonSerializer.Serialize(writer, value, value.GetType(), options); } } ``` And I registered the converter like this: ```csharp var options = new JsonSerializerOptions(); options.Converters.Add(new AnimalConverter()); ``` However, when I try to deserialize using: ```csharp var animals = JsonSerializer.Deserialize<List<Animal>>(jsonString, options); ``` I get the behavior `InvalidOperationException: want to convert JSON to target type 'System.Type'`. It seems like the deserializer want to determine the type due to the way I’m trying to handle it. I’ve also verified that the JSON string is correctly formatted. Any guidance on how to correctly set up polymorphic deserialization with `System.Text.Json` would be greatly appreciated! This is part of a larger CLI tool I'm building. Thanks in advance! The stack includes C# and several other technologies.