JSON Schema - can array / list validation be combined with anyOf? - visual-studio-code

Question

I have a json document I'm trying to validate with this form:
...
"products": [{
"prop1": "foo",
"prop2": "bar"
}, {
"prop3": "hello",
"prop4": "world"
},
...
There are multiple different forms an object may take. My schema looks like this:
...
"definitions": {
"products": {
"type": "array",
"items": { "$ref": "#/definitions/Product" },
"Product": {
"type": "object",
"oneOf": [
{ "$ref": "#/definitions/Product_Type1" },
{ "$ref": "#/definitions/Product_Type2" },
...
]
},
"Product_Type1": {
"type": "object",
"properties": {
"prop1": { "type": "string" },
"prop2": { "type": "string" }
},
"Product_Type2": {
"type": "object",
"properties": {
"prop3": { "type": "string" },
"prop4": { "type": "string" }
}
...
On top of this, certain properties of the individual product array objects may be indirected via further usage of anyOf or oneOf.
I'm running into issues in VSCode using the built-in schema validation where it throws errors for every item in the products array that don't match Product_Type1.
So it seems the validator latches onto that first oneOf it found and won't validate against any of the other types.
I didn't find any limitations to the oneOf mechanism on jsonschema.org. And there is no mention of it being used in the page specifically dealing with arrays here: https://json-schema.org/understanding-json-schema/reference/array.html
Is what I'm attempting possible?

Answer 1

Your general approach is fine. Let's take a slightly simpler example to illustrate what's going wrong.
Given this schema
{
"oneOf": [
{ "properties": { "foo": { "type": "integer" } } },
{ "properties": { "bar": { "type": "integer" } } }
]
}
And this instance
{ "foo": 42 }
At first glance, this looks like it matches /oneOf/0 and not oneOf/1. It actually matches both schemas, which violates the one-and-only-one constraint imposed by oneOf and the oneOf fails.
Remember that every keyword in JSON Schema is a constraint. Anything that is not explicitly excluded by the schema is allowed. There is nothing in the /oneOf/1 schema that says a "foo" property is not allowed. Nor does is say that "foo" is required. It only says that if the instance has a keyword "foo", then it must be an integer.
To fix this, you will need required and maybe additionalProperties depending on the situation. I show here how you would use additionalProperties, but I recommend you don't use it unless you need to because is does have some problematic properties.
{
"oneOf": [
{
"properties": { "foo": { "type": "integer" } },
"required": ["foo"],
"additionalProperties": false
},
{
"properties": { "bar": { "type": "integer" } },
"required": ["bar"],
"additionalProperties": false
}
]
}