JSON-schema: value based on oneOf - json

Question

I have the following json-schema which defines 3 types of toys, to be used with this json GUI builder (github):
{
"id": "http://some.site.somewhere/entry-schema#",
"$schema": "http://json-schema.org/draft-04/schema#",
"description": "schema for toys in game",
"type": "object",
"required": [ "type" ],
"properties": {
"sawObj": {
"type": "object",
"oneOf": [
{ "$ref": "#/definitions/rect" },
{ "$ref": "#/definitions/circle" },
{ "$ref": "#/definitions/img" }
]
}
},
"definitions": {
"rect": {
"properties": {
"width": { "type": "integer" },
"height": { "type": "integer" },
"weight": { "type": "integer" }
},
"required": [ "width", "height", "weight" ],
"additionalProperties": false
},
"circle": {
"properties": {
"radius": { "type": "integer" },
"weight": { "type": "integer" }
},
"required": [ "radius", "weight" ],
"additionalProperties": false
},
"img": {
"properties": {
"path": { "type": "string" },
"width": { "type": "integer" },
"height": { "type": "integer" },
"weight": { "type": "integer" }
},
"required": [ "path", "width", "height", "weight" ],
"additionalProperties": false
}
}
}
If I pick the circle object for example I get an output:
{
"sawObj": {
"radius": 0,
"weight": 0
}
}
I want to add a value "type" which would always be constrained to reflect the users chosen type. So instead something like this:
{
"sawObj": {
"type": "circle",
"radius": 0,
"weight": 0
}
}
Where the type is automatically determined by the users choice from the oneOf properties section.
How can I do this with json-schema?

Answer 1

I was able to do this the enum value and only allowing a single value representing the type. I also set the type value as required so it is always automatically set to 'circle'.
"circle": {
"properties": {
"radius": {
"type": "integer"
},
"weight": {
"type": "integer"
},
"type": {
"type": "string",
"enum": ["circle"]
}
},
"required": ["radius", "weight", "type"],
"additionalProperties": false
}
Note: I want to point out this solution is not ideal. I'm hoping to find a better way to do this.