Supported discriminator in oneOf with nested allOf

[mefellows]

Background

Ajv does not support oneOf(allOf(...), allOf(...))

See ajv/lib/vocabularies/discriminator/index.ts

The documented limitation is here: https://ajv.js.org/json-schema.html#discriminator:

each oneOf subschema must have properties keyword with discriminator property. The subschemas should be either inlined or included as direct references (only $ref keyword without any extra keywords is allowed).

Workaround

A workaround is to flatten the inner allOf()s.

Repro

Below is effectively the code that gets executed. You can run this file directly in Node.js.

import Ajv from "ajv/dist/2019.js";

const payload = {
  type: "ADD_EVENT",
  payload: {
    events: [
      {
        type: "EVENT_TYPE_A",
        payload: {
          originator: "ORIGINATOR_A",
        },
      },
    ],
  },
};

const originalSchema = {
  type: "object",
  properties: {
    type: {
      const: "ADD_EVENT",
    },
    payload: {
      type: "object",
      properties: {
        events: {
          type: "array",
          items: {
            type: "object",
            properties: {
              type: {
                const: "EVENT_TYPE_A",
              },
              payload: {
                type: "object",
                oneOf: [
                  {
                    type: "object",
                    allOf: [
                      {
                        type: "object",
                        properties: {
                          originator: {
                            const: "ORIGINATOR_A",
                          },
                        },
                        required: ["originator"],
                      },
                    ],
                  },
                  {
                    type: "object",
                    allOf: [
                      {
                        type: "object",
                        properties: {
                          originator: {
                            const: "ORIGINATOR_B",
                          },
                        },
                        required: ["originator"],
                      },
                    ],
                  },
                ],
                discriminator: {
                  propertyName: "originator",
                },
              },
            },
            required: ["type", "payload"],
          },
        },
      },
    },
  },
};

const modifiedSchema = {
  type: "object",
  properties: {
    type: {
      const: "ADD_EVENT",
    },
    payload: {
      type: "object",
      properties: {
        events: {
          type: "array",
          items: {
            type: "object",
            properties: {
              type: {
                const: "EVENT_TYPE_A",
              },
              payload: {
                type: "object",
                oneOf: [
                  {
                    type: "object",
                    properties: {
                      originator: {
                        const: "ORIGINATOR_A",
                      },
                    },
                    required: ["originator"],
                  },
                  {
                    type: "object",
                    properties: {
                      originator: {
                        const: "ORIGINATOR_B",
                      },
                    },
                    required: ["originator"],
                  },
                ],
                discriminator: {
                  propertyName: "originator",
                },
              },
            },
            required: ["type", "payload"],
          },
        },
      },
    },
  },
};

const ajv = new Ajv({
  allErrors: true,
  discriminator: true,
  strictSchema: false,
});
ajv.validate(modifiedSchema, payload); // this is ok
ajv.validate(originalSchema, payload); // this throws