Discriminator logic will not dereference schemas before validating preconditions

[ggoodman]

What version of Ajv you are you using?

8.0.5

What problem do you want to solve?

Defer the evaluation of precondition checks on discriminators after dereferencing $refs. Currently, a schema will fail validation if the list of oneOf children contains a referenced schema instead of an embedded schema.

See:

ajv/lib/vocabularies/discriminator/index.ts

Lines 64 to 72 in baf1475

	for (let i = 0; i < oneOf.length; i++) {
	const sch = oneOf[i]
	const propSch = sch.properties?.[tagName]
	if (typeof propSch != "object") {
	throw new Error(`discriminator: oneOf schemas must have "properties/${tagName}"`)
	}
	tagRequired = tagRequired && (topRequired || hasRequired(sch))
	addMappings(propSch, i)
	}

What do you think is the correct solution to problem?

The preconditions for discriminator support should be deferred.

Will you be able to implement it?

I don't think so. 😬

[nabati]

Bumping into a similar (?) issue as well.

Even if you embed the schema but you use compound keyword, it will throw a validation error.

Will work:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "discriminator": {
    "propertyName": "moduleType"
  },
  "oneOf": [
    {
      "properties": {
        "moduleType": {
          "const": "cards"
        }
      }
    },
    {
      "properties": {
        "moduleType": {
          "const": "chart"
        }
      }
    }
  ],
  "required": ["moduleType"]
}

Wont work:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "discriminator": {
    "propertyName": "moduleType"
  },
  "oneOf": [
    {
      "allOf": [
        {
          "properties": {
            "moduleType": {
              "const": "cards"
            }
          }
        }
      ]
    },
    {
      "allOf": [
        {
          "properties": {
            "moduleType": {
              "const": "chart"
            }
          }
        }
      ]
    }
  ],
  "required": ["moduleType"]
}