add property to object with additionalProperties: false from switch

[mbroadst]

should this be possible:

{
  type: 'object',
  properties: {
    foo: { type: 'array', minItems: 2 },
    bar: { type: 'string' }
  },
  additionalProperties: false,
  required: [ 'foo', 'bar' ],
  switch: [{
    if: { properties: { bar: { constant: 'testing } } },
    then: {
      properties: { baz: { type: 'string' } },
      required: [ 'foo', 'bar', 'baz' ]
    }
  }]
}

It seems unclear from the documentation, but shouldn't I technically be able to even set additionalProperties: true in the switch's then?

[epoberezkin]

additionalProperties are scoped to the current schema, they don't have global visibility...

In this case it means that additionalProperties will fail validation if any property in addition to foo and bar is present. You cannot extend it by declaring properties in another schema object, they should be declared in the same schema object. That's by the spec.

You need:

{
  type: 'object',
  properties: {
    foo: { type: 'array', minItems: 2 },
    bar: { type: 'string' }
    baz: { type: 'string' },
  },
  additionalProperties: false,
  required: [ 'foo', 'bar' ],
  switch: [
    {
      if: { properties: { bar: { constant: 'testing' } } },
      then: {
        required: [ 'baz' ]
      }
    },
    {
      then: { not: { required: ['baz'] } }
    }
  ]
}

[epoberezkin]

See #129, #134, #140

[epoberezkin]

And you don't need v5 switch for that, oneOf will work too.

[epoberezkin]

Maybe it will all make more sense if you think about it in this way: JSON Schema may seem like it is about declaring what is allowed, but it is not. JSON Schema is about imposing restrictions. So you can easily extend the restrictions by adding them to any schema (like in the case with required above, where you don't need to repeat properties required in another schema object). But you cannot reduce the restriction by adding something to another schema object (like adding property declaration to another schema in your example). To reduce the restriction you need to modify the schema that imposed the restriction (or to use anyOf/oneOf). Not sure if I made it any clearer to be honest...

[mbroadst]

@epoberezkin no you've been quite clear, I think it was I who was not so clear in the initial case. What I'm looking for here is to explicitly disallow baz in case the value of bar === testing. I haven't been able to sort out how to get that working yet, other than providing whole separate schemas and using oneOf

[epoberezkin]

you can use not with required as in my example to prohibit proberty

[mbroadst]

oh really? I had thought that would just remove it from the required list, that's a bit of a semantic misnomer I'd say as the negation of requirement isn't necessarily prohibition 😄

Totally works, thank you very much for your help

[epoberezkin]

not negates validation result. not passes when schema inside fails. required fails when property is absent.

[epoberezkin]

But semantically it is funny indeed

[mbroadst]

it might make sense to suggest an alias present for required (to the json-schema spec maintainers that is). This is far more readable imho:

then: { not: { present: [ 'baz' ] } }

[epoberezkin]

You don't have to wait for the standard change :)

ajv.addKeyword('present', {
  macro: (schema) => ({ required: schema });
});