C# How to handle polymorphic models using NSwag

Question

I have a polymorphic model:

public class CreateOrderRequest
{
    public List<CreateOrderItem> OrderItems { get; set; } 
}

/// <summary>
/// Identifies a new item within an order
/// </summary>    
[JsonConverter(typeof(CreateOrderLineJsonConvertor))]
[KnownType("GetKnownTypes")]
public class CreateOrderItem
{
    public string OrderContext { get; set; }
    public string OrderItemType { get; set; }

    public static Type[] GetKnownTypes()
    {
        return new[]
        {
            typeof(OrderItemType1), typeof(OrderItemType2)
        };
    }
}

public class OrderItemType1: CreateOrderItem
{
     public string Type1Prop {get;set;}
}

public class OrderItemType2: CreateOrderItem
{
     public string Type2Prop {get;set;}
}

Using NSwag (NSwag.AspNetCore) according to the documentation, I expected this to be enough so that documentation indicated / contained the order item types? But no...

Have i completely missed the point of what NSwag requires? I have the OrderItemType property. Do i need to get a discriminator involved? Where is this documented?

TIA

Answer 1

You need

[JsonConverter(typeof(JsonInheritanceConverter), "discriminator")]

on the base class so that the discriminator is added.

See https://github.com/RSuter/NJsonSchema/wiki/Inheritance

Answer 2

I used the answer by Rico Suiter as a starting point. JSON objects got correct discriminator field, but polymorphic description was missing from swagger.json contract.

Swagger annotations to fix the issue:

[JsonConverter(typeof(JsonInheritanceConverter), "discriminator")]
[SwaggerDiscriminator("discriminator")]
[SwaggerSubType(typeof(ChildDto1))]
[SwaggerSubType(typeof(ChildDto2))]
[SwaggerSubType(typeof(ChildDto3))]
public abstract class BaseDto
{
    public int BaseProperty { get; set; }
}

Also turned on annotations in Startup.cs:

services.AddSwaggerGen(c =>
{
    c.EnableAnnotations(true, true);
    ...
}

Used Swashbuckle.AspNetCore.Annotations v6.1.0 package