JsonPolymorphism

Easily add System.Text.Json serialization support for polymorphic models in C# / .NET 5. Works by generating a JsonConverter tailored to your class/record at compile-time and attaching it via JsonConverterAttribute. All you need is a discriminator property on your base types marked with the new JsonDiscriminator attribute

Install

Since this project relies on Source Code Generation, this project can only be used with C# (not F#) projects targeting net5.0.

dotnet add package Wivuu.JsonPolymorphism

Usage

The JsonDiscriminator attribute can be attached to either a record parameter or class/record property. Once attached the type of that discriminator will be used to find all classes which derive from your base type. Any enum types without a corresponding inherited type will result in a compile-time error.

enum AnimalType
{
    Insect,
    Mammal,
    Reptile,
    Bird // <- This causes an easy to understand build error if it's missing a corresponding inherited type!
}

// My base type is 'Animal'
abstract partial record Animal( [JsonDiscriminator] AnimalType type, string Name );

// Animals with type = 'Insect' will automatically deserialize as `Insect`
record Insect(int NumLegs = 6, int NumEyes=4) : Animal(AnimalType.Insect, "Insectoid");

record Mammal(int NumNipples = 2) : Animal(AnimalType.Mammal, "Mammalian");

record Reptile(bool ColdBlooded = true) : Animal(AnimalType.Reptile, "Reptilian");

Serialize and Deserialize with ease!

Make sure to use consistent JsonSerializerOptions; Currently the discriminator value when deserializing is case-sensitive.

JsonSerializerOptions options = new();

Animal[] animals = 
{
    new Insect(NumLegs: 8, NumEyes: 6),
    new Mammal(NumNipples: 6),
    new Reptile(ColdBlooded: false),
};

var serialized          = JsonSerializer.Serialize(animals, options);
var animalsDeserialized = JsonSerializer.Deserialize<Animal[]>(serialized, options);

if (animalsDeserialized is null)
    throw new System.Exception("Unable to deserialize");
    
Assert.Equal(animals.Length, animalsDeserialized.Length);

for (var i = 0; i < animals.Length; ++i)
    Assert.Equal(animals[i], animalsDeserialized[i]);