Polymorphic Endpoint Validation Fails in ApiDog Despite Correct OpenAPI (oneOf + Discriminator)

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1

I have an endpoint setup with polymorphic types.

In the generated swagger.json, the polymorphism is described as follows:

"oneOf": [
  { "$ref": "#/components/schemas/SchemaA" },
  { "$ref": "#/components/schemas/SchemaB" },
  ...
],
"discriminator": {
  "propertyName": "$type",
  "mapping": {
    "identifier1": "#/components/schemas/SchemaA",
    "identifier2": "#/components/schemas/SchemaB",
    ...
  }
}

Thus:
The payload includes a $type property to identify the actual type.
Each $type maps to a specific schema reference under components/schemas.

Problem
When calling the endpoint via ApiDog (with a valid response payload including $type), the ApiDog validation fails.

The reported errors are:
“Additional properties not allowed”
“Missing required properties”

These errors occur even though:
The response payload matches the expected polymorphic type based on $type.
The Swagger/OpenAPI definition has the correct discriminator and oneOf entries.

2

Hi Jens , thanks for reaching out, we will look into this issue and get back to you soon.

3

Hello Jens, Based on the information you provided, it’s unclear whether the involved models have additionalProperties: false defined. To investigate further, could you share:

  1. The JSON schema of the model that was matched (based on $type).
  2. The actual response payload.
  3. The specific fields mentioned in the errors (“Additional properties not allowed” / “Missing required properties”).
    This will help us pinpoint the issue. Thanks!