Schema array type with anyOf and discriminator fails validation

[rwrife]

I'm trying to validate an OpenAPI document that contains a schema object that is of type 'array' that can be an 'anyOf' that uses a discriminator to know which object goes into the array and it's failing validation. The document appears to be a valid OAS3 document and the Swagger UI has no issues rendering it, so I'm guessing it's an issue with OpenAPI.NET.

I'm getting validation errors similar to:

Composite Schema ChildTypeA must contain property specified in the discriminator type. [#/components/schemas/SampleResponse/properties/suggestedActions/items/anyOf]
Composite schema ChildTypeA must contain property specified in the discriminator type in the required field list. [#/components/schemas/SampleResponse/properties/suggestedActions/items/anyOf]

...for this document

openapi: 3.0.0
info:
  description: Service to test discriminator
  version: 1.0.0
  title: Test Service
servers:
  - url: 'https://localhost'
paths:
  /test:
    post:
      description: Sample post of SampleRequest
      requestBody:
        description: Returns the SampleResponse with multiple types
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/SampleRequest'
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/SampleResponse'
components:
  schemas:
    SampleRequest:
      type: object
      required:
        - id
      properties:
        id:
          type: string
          description: Random ID
          example: '1513776099991'
    BaseType:
      type: object
      required:
        - type
      properties:
        type:
          type: string
          description: Suggested object type
    ChildTypeA:
      allOf:
        - $ref: '#/components/schemas/BaseType'
          properties:
            type:
              type: string
              enum:
                - typeA
      type: object
    ChildTypeB:
      allOf:
        - $ref: '#/components/schemas/BaseType'
          properties:
            type:
              type: string
              enum:
                - typeB
      type: object
    SampleResponse:
      type: object
      properties:
        suggestedActions:
          type: array
          items:
            anyOf:
              - $ref: '#/components/schemas/ChildTypeA'
              - $ref: '#/components/schemas/ChildTypeB'
            discriminator:
              propertyName: type

[PerthCharern]

I think currently that rule only looks at the properties in the schema itself without delving into the properties in the anyOf/allOf. This is a bug in our validator.

[ma499]

Are there any plans to fix this bug? This validator is now being used by Azure API Management when deploying APIs, and we are no longer able to deploy updates to our existing API to production because of this problem.

[Robzilla]

Yes reported last November. Pretty big impact for me too. Apparently a fix is rolling out next week. See #429
Bit scary when something this big stops deployments for a few months.

[fabich]

@PerthCharern any updates on this?

[ma499]

Is this actually a bug? I just read the relevant section of the latest Open API 3.0.3 specification which indicates that a discriminator field is actually required to be a 'required' field.

To support polymorphism, the OpenAPI Specification adds the discriminator field. When used, the discriminator will be the name of the property that decides which schema definition validates the structure of the model. As such, the discriminator field MUST be a required field. There are two ways to define the value of a discriminator for an inheriting instance.

This is not new, the same is specified for Open API 2.0.

Therefore, having read the specification, and thinking about the semantics of a discriminator field, I would argue that OpenAPI.NET's behaviour is actually correct and the official OpenAPI/Swagger parsers are the ones that actually have the bug as they are not strict enough to identify this problem.

I realise I hadn't understood the issue properly and this is indeed a bug in the parser that it is not traversing the anyOf link to look in the child schemas for the required discriminator field.

[himanigulati]

Is this issue still Open? We are dealing with the similar problem.

[amrith92]

@himanigulati Yes, I think this is still open.

[darrelmiller]

Ok, I must be doing something wrong. I'm trying the above sample in the OpenAPIWorkbench tool from the master branch and I am not seeing the error...

[darrelmiller]

I verified this again and I am not seeing any errors. Please re-open if you find this is still a problem.