Does not pick up default value if defined in $ref definition

[onury]

What version of Ajv are you using? Does the issue happen if you use the latest version?
4.8.2

Ajv options object (see https://github.com/epoberezkin/ajv#options):

{
    allErrors: true,
    format: 'full',
    useDefaults: true
}

JSON Schema (please make it as small as possible to reproduce the issue):

{
    ...
    "properties": {
        "phone": {
            "$ref": "#/definitions/optionalPhone"
        },
       ...
    },
    "definitions": {
        "emptyString": {
            "type": "string",
            "maxLength": 0
        },
        "optionalPhone": {
            "anyOf": [
                { "format": "phone" },
                { "$ref": "#/definitions/emptyString" }
            ],
            "default": ""
        }
    }
}

Above will work only if I define default: "" within phone.

Data (please make it as small as posssible to reproduce the issue):

{}

Validation result, data AFTER validation, error messages:
Data after validation: {}
No errors. Just the default value is not set for phone.

What results did you expect?
{ phone: "" }

[epoberezkin]

Yes, only from items and properties directly at the moment. It's a documented limitation: https://github.com/epoberezkin/ajv#assigning-defaults

[dinvlad]

Are there plans to apply defaults from references as well?

[epoberezkin]

I see it as "nice to have" rather than something many users need. And it's quite complex. So there are no plans to implement it at the moment.

[epoberezkin]

Even if you define properties in $refs, you can still define default values for the properties alongside $refs rather than inside: https://runkit.com/esp/5942f60cc72ffe0012805f9c

[dinvlad]

Thanks, I've tried that before but incorrectly (through allOf), which is why it wasn't working. IMO that's actually better than through Definitions.

[epoberezkin]

through allOf it also works (unless you put default inside allOf). And it's not that putting default inside allOf is incorrect, it's just unsupported...

[dinvlad]

Yep, that's exactly what I've tried. Thanks again - I think it's even cleaner without allOf.

[marshall007]

@epoberezkin this seems especially bad in the case of $merge (see ajv-validator/ajv-merge-patch#16). I was attempting to use ajv-merge-patch to avoid the subtleties in using $ref with things like additionalProperties and default. It was working great until I realized that default values weren't being applied.

Can you explain why this is still an issue when using $merge/$patch? My assumption was that the internal representation would be flatly merged (and thus the default and dynamicDefaults keywords would behave as expected).

Example Schema

{
  $id: 'activities.create',
  $merge: {
    source: {
      $ref: 'base.create',
    },
    with: {
      type: 'object',
      required: [
        'entitySubType',

        'name',
        'endDateTime',
        'startDateTime',
      ],
      additionalProperties: false,
      properties: {
        attributes: {
          type: 'object',
          default: {},
        },
        entityType: {
          type: 'string',
          const: EntityType.ACTIVITY,
          default: EntityType.ACTIVITY,
        },
        entitySubType: {
          $ref: 'types#/definitions/activityType',
        },
        name: { type: 'string' },
        endDateTime: {
          type: 'string',
          format: 'date-time',
        },
        startDateTime: {
          type: 'string',
          format: 'date-time',
        },
      },
    },
  },
}

In the above schema, neither the defaults from the referenced base.create schema nor the with block are applied.

[epoberezkin]

@marshall007 This question belongs in ajv-merge-patch. $merge is implemented as a custom keyword, it doesn't merge anything into the original schema. I don't plan to improve it until json-schema-org standardises it (or some other re-use mechanism).