Defining conditional attributes in OpenAPI

(Copying my answer from Stack Overflow)

To define oneOf/anyOf logic for request parameters, you would have to define all parameters as a single object-type parameter, as explained here.

parameters:
  - in: query
    name: params  # This name will NOT appear in the request URL
                  # but will be used in generated client SDKs / server stubs
    required: true

    # serialize this object as ?key1=value1&key2=value2
    style: form
    explode: true

    schema:
      type: object
      properties:
        longitude: { ... }
        latitude:  { ... }
        postalCode:  { ... }
        countryCode: { ... }
        city:  { ... }
        state: { ... }
      anyOf:
        - required: [longitude, latitude]
        - required: [postalCode, countryCode]
        - required: [city, state, countryCode]

Note that OpenAPI 3.0 does not support the dependencies keyword of JSON Schema, but it's supported in OpenAPI 3.1 (the latest version).

There's also an existing feature request in the OpenAPI Specification repository to support dependencies between individual parameter definitions.