compileAsync does not loadSchema a schema that is $ref’d by a oneOf with a discriminator

[yonran]

What version of Ajv are you using? Does the issue happen if you use the latest version?

latest (8.13.0)

Ajv options object

const options = {
  discriminator: true,
  async loadSchema(url) {
    console.log('loadSchema', url)
    const name = url.substring("scheme://".length)
    return schemas[name]
  },
};

JSON Schema

const schemas = {
  main: {
    type: "object",
    discriminator: {propertyName: "foo"},
    required: ["foo"],
    oneOf: [
      {
        $ref: "scheme://schema1",
      },
      {
        $ref: "scheme://schema2",
      },
    ],
  },
  schema1: {
    type: "object",
    properties: {
      foo: {const: "x"},
    },
  },
  schema2: {
    type: "object",
    properties: {
      foo: {enum: ["y", "z"]},
    },
  },
};

Sample data

{"foo": "x"}

Your code

const Ajv = require("ajv");
const ajv = new Ajv(options);
// If you uncomment this, then there is no error
// Object.entries(schemas).forEach(([id, schema]) => {
//   ajv.addSchema(schema, 'scheme://' + id)
// })
async function main() {
  const validate = await ajv.compileAsync(schemas.main)
  validate(data)
}
main().catch((err) => console.log(err))

Validation result, data AFTER validation, error messages

Error: discriminator: oneOf subschemas (or referenced schemas) must have "properties/foo"

What results did you expect?
No error

Are you going to resolve the issue?
Maybe if it is easy

Notes:

• If you call ajv.addSchema (i.e., uncomment the commented code), then the error goes away. Therefore, it is the resolving of the $ref that is the issue

• When discriminator: true, then loadSchema is not called.

• But if you set discriminator: false and remove the discriminator from schema.main, then loadSchema is called.

  loadSchema scheme://schema1
  loadSchema scheme://schema2
  

My guess is that lib/vocabularies/discriminator/index.ts’s getMapping() needs to throw new MissingRefError so that _compileAsync can catch the error and load the missing schemas.

[jasoniangreen]

Hi @yonran thanks for raising this, I have setup your example and it does look like it could be a bug. Since you responded "Maybe if it is easy" I'll ask if you would like to have a go at submitting a PR? Either way I will look into this and consider it a bug for now.

[mathieubathalon]

lib/commands/query.js

[mathieubathalon]

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