Template generation for arrays with `anyOf` clobbers valid default values using first schema's template

[snoozbuster]

Given the following schema listSchemaWithDefault:

{
  "type": "object",
  "properties": {
    "someList": {
      "type": "array",
      "items": { "anyOf": [{ "a": "number" }, { "b": "string" }, { "c": { "const": "foo" } }] },
      "minItems": 3,
      "default": [
        { "a": 1 },
        { "b": "schfifty-five" },
        { "c": "foo" }
      ]
    }
  }
}

calling new Draft07(listSchemaWithDefault).getTemplate() will return something to the effect of:

{
  "someList": [
    { "a": 1 },
    { "a": 0, "b": "schfifty-five" }
    { "a": 0, "c": "foo" }
  ]
}

(furthermore, as an additional and separate issue, these objects are permanently overwritten in the original schema object as an unavoidable side-effect.)

The expected behavior in this case would be to return the default value as-is, as each object is valid according to one of the schemas in anyOf. Additionally, if the middle schema in the anyOf was modified to { "required": ["b", "f"], "b": "string", "f": { "const": "bar" } }, I would expect that the middle object would be returned from getTemplate as { "b": "schfifty-five", "f": "bar" } (without modifying the original value).

My understanding is the getSchema function already has the ability to a piece of data to a specific schema that is present in an anyOf (as per the docs):

In this case, as I understand it, calling new Draft07(listSchemaWithDefault).getSchema('/someList/1', listSchemaWithDefault.properties.someList.default) would return the value { "b": "string" } as expected. Therefore, my belief is that the bug lies in getTemplateSchema - instead of always taking the first item, it should attempt to resolve the passed in data to the matching schema from the anyOf using the same technique as in getSchema.

[sagold]

Hi snoozbuster,

I agree. For the example above, we would expect

{
  "someList": [
    { "a": 1 },
    { "b": "schfifty-five" },
    { "c": "foo" }
  ]
}

The other issue you mention is, that the schema from new Draft07(listSchemaWithDefault).getSchema().properties.someList.default is modified and every item contains an a property?

I will look into it!

[sagold]

Testing this, this issue has been already fixed in the upcoming version 8, which can currently be installed using json-schema-library@8.0.0-rc6. I working towards a full v8 release in the next weeks. If you go for this package, be aware of the breaking changes:

• Renamed JSON to Json in exported names, mainly: JSONError to JsonError and JSONSchema to JsonSchema
• getTemplate only adds required properties. Can be changed by setting addOptionalProps:true

References

• branch: https://github.com/sagold/json-schema-library/tree/develop
• test: https://github.com/sagold/json-schema-library/blob/develop/test/unit/issues/issue38.getTemplate.anyOf.test.ts
• testresult: https://github.com/sagold/json-schema-library/runs/14708670439#r0s0

[sagold]

json-schema-library@8.0.0 has been released to npm and includes a fix for this issue.