JSONSchema v4 - Error when resolving schema reference - Definitions and References - jsonschema

Question

When trying to validate the following schema using http://www.jsonschemavalidator.net/,
{
"id": "http://some.site.somewhere/entry-schema#",
"$schema": "http://json-schema.org/draft-04/schema#",
"description": "schema for the FormularSpecification",
"definitions": {
"elementId": {
"id": "http://jsonschema.net/elementId",
"type": "string"
},
"mappingKey": {
"id": "http://jsonschema.net/mappingKey",
"type": "string"
},
"elementType": {
"id": "http://jsonschema.net/elementType",
"type": "string"
},
"length": {
"id": "http://jsonschema.net/length",
"type": "integer"
},
"label": {
"id": "http://jsonschema.net/label",
"type": "string"
},
"content": {
"id": "http://jsonschema.net/content",
"type": "string"
},
"placeholder": {
"id": "http://jsonschema.net/placeholder",
"type": "string"
},
"date": {
"id": "http://jsonschema.net/date",
"type": "string"
},
"option": {
"id": "http://jsonschema.net/option",
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"label": { "$ref": "#/definitions/label" }
},
"required": ["elementId", "label"]
},
"options": {
"id": "http://jsonschema.net/options",
"type": "array",
"items": { "$ref": "#/definitions/option" },
"minItems": 1,
"uniqueItems": true
},
"textfield": {
"id": "http://jsonschema.net/textfield",
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"length": { "$ref": "#/definitions/length" },
"label": { "$ref": "#/definitions/label" },
"placeholder": { "$ref": "#/definitions/placeholder" },
"textfieldType": {
"enum": [ "text", "ext4", "btrfs" ]
}
},
"required": ["elementId", "length", "label", "placeholder", "textfieldType"]
},
"checkbox": {
"id": "http://jsonschema.net/checkbox",
"type": "object",
"properties": {
"label": { "$ref": "#/definitions/label" }
},
"required": ["label"]
},
"radio": {
"id": "http://jsonschema.net/radio",
"type": "object",
"properties": {
"label": { "$ref": "#/definitions/label" },
"options": { "$ref": "#/definitions/options" }
},
"required": ["label", "options"]
},
"dropdown": {
"id": "http://jsonschema.net/dropdown",
"type": "object",
"properties": {
"label": { "$ref": "#/definitions/label" },
"options": { "$ref": "#/definitions/options" }
},
"required": ["label", "options"]
},
"validator": {
"id": "http://jsonschema.net/validator",
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" }
}
},
"validators": {
"id": "http://jsonschema.net/validators",
"type": "array",
"items": { "$ref": "#/definitions/validator" }
},
"interactiveDetails": {
"type": "object",
"oneOf": [
{ "textfield": { "$ref": "#/definitions/textfield" } },
{ "checkbox": { "$ref": "#/definitions/checkbox" } },
{ "radio": { "$ref": "#/definitions/radio" } },
{ "dropdown": { "$ref": "#/definitions/dropdown" } },
{ "date": { "$ref": "#/definitions/date" } }
]
},
"interactive": {
"id": "http://jsonschema.net/interactive",
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"elementType": { "$ref": "#/definitions/elementType" },
"mappingKey": { "$ref": "#/definitions/mappingKey" },
"validators": { "$ref": "#/definitions/validators" },
"interactiveDetails" : { "$ref": "#/definitions/interactiveDetails" }
},
"required": ["elementId", "elementType", "mappingKey", "validators"]
},
"interactives": {
"id": "http://jsonschema.net/interactives",
"type": "array",
"items": { "$ref": "#/definitions/interactive" }
},
"description": {
"id": "http://jsonschema.net/description",
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"elementType": { "$ref": "#/definitions/elementType" },
"content": { "$ref": "#/definitions/content" }
},
"required": ["elementId", "elementType", "content"]
},
"descriptions": {
"items": { "$ref": "#/definitions/description" }
},
"children": {
"items": {
"anyOf": [
{ "$ref": "#/definitions/group" },
{ "$ref": "#/definitions/question" }
]
},
"minItems": 1
},
"question": {
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"descriptions": { "$ref": "#/definitions/descriptions" },
"interactives": { "$ref": "#/definitions/interactives" }
},
"required": ["elementId", "descriptions", "interactives"]
},
"group": {
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"descriptions": { "$ref": "#/definitions/descriptions" },
"children": { "$ref": "#/definitions/children"}
},
"required": ["elementId", "descriptions", "children"]
}
},
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"description": { "$ref": "#/definitions/descriptions" },
"children": { "$ref": "#/definitions/children" }
},
"required": [
"elementId",
"descriptions",
"children"
]
}
I'm getting the following error:
Error when resolving schema reference '#/definitions/elementId'. Path 'definitions.description.properties.elementId', line 135, position 30.
I cannot figure out what the problem is. I scanned the documentation several times and had a look at tutorials, but I do not have any clue.

Answer 1

The semantics of the id keyword are are a bit confusing. I'm not sure I completely understand it myself. In general it is almost never a good idea to include id anywhere other than the root of your schema.
The "id" keyword (or "id", for short) is used to alter the resolution scope. When an id is encountered, an implementation MUST resolve this id against the most immediate parent scope. The resolved URI will be the new resolution scope for this subschema and all its children, until another id is encountered.
http://json-schema.org/latest/json-schema-core.html#anchor27
Consider the following excerpt from you schema. Because you include the id keyword, your "elementId" and "label" $refs don't resolve against the root of the document as you expect, they resolve from the nearest parent schema id.
"option": {
"id": "http://jsonschema.net/option",
"type": "object",
"properties": {
"elementId": { "$ref": "#/definitions/elementId" },
"label": { "$ref": "#/definitions/label" }
},
"required": ["elementId", "label"],
"definitions": { ... } <-- your $refs expect values here
}
},
I have seen that in some circles, people write schemas with ids for every subschema. I'm not sure what benefit they think they are getting out of doing that, but I suspect that they think of id as just a label and don't understand how it alters resolution scope.
If you do have good reason to use ids everywhere and want to leave them in, you can always explicitly reference the root id when you have a conflict.
{ "$ref": "http://some.site.somewhere/entry-schema#definitions/elementId" }