Inheritance bug: wrong use of JsonDerivedTypeAttribute is required

[PeterDraex]

Microsoft docs expects the JsonDerivedType attribute to be applied to the base type:

[JsonDerivedType(typeof(WeatherForecastWithCity))]
public class WeatherForecastBase
{
    public DateTimeOffset Date { get; set; }
    public int TemperatureCelsius { get; set; }
    public string? Summary { get; set; }
}
public class WeatherForecastWithCity : WeatherForecastBase
{
    public string? City { get; set; }
}

But to generate a usable TypeScript code with NSwag, you must put the annotation on both the base and derived types:

[JsonDerivedType(typeof(WeatherForecastWithCity), typeDiscriminator: "this-must-be-specified-but-is-ignored")]
[JsonDerivedType(typeof(WeatherForecastWithVillage), typeDiscriminator: "this-must-be-specified-but-is-ignored2")]
public abstract class WeatherForecastBase
{
    public DateTimeOffset Date { get; set; }
    public int TemperatureCelsius { get; set; }
    public string? Summary { get; set; }
}

[JsonDerivedType(typeof(WeatherForecastWithCity), typeDiscriminator: "this-must-be-specified-but-is-ignored")]
public class WeatherForecastWithCity : WeatherForecastBase
{
    public string? City { get; set; }
}

[JsonDerivedType(typeof(WeatherForecastWithVillage), typeDiscriminator: "this-must-be-specified-but-is-ignored2")]
public class WeatherForecastWithVillage : WeatherForecastBase
{
    public string? Village { get; set; }
}

Only then you get the correct TypeScript:

export interface WeatherForecastBase {
    Date: string;
    TemperatureCelsius: number;
    Summary: string | null;
    $type: string;
}

export interface WeatherForecastWithCity extends WeatherForecastBase {
    City: string | null;
    $type: 'WeatherForecastWithCity';
}

export interface WeatherForecastWithVillage extends WeatherForecastBase {
    Village: string | null;
    $type: 'WeatherForecastWithVillage';
}

[david-brink-talogy]

Aren't you missing [JsonPolymorphic]?

Perhaps these tests are insufficient, but they don't have the extra [JsonDerivedType].

NJsonSchema/src/NJsonSchema.Tests/Generation/SystemTextJson/SystemTextJsonInheritanceTests.cs

Line 92 in 7c39559

[JsonDerivedType(typeof(Apple2), "a")]