Enforce object non emptyness using json schema

Question

We can enforce empty attribute of type object as follows:

{
   "description": "voice mail record",
   "type": "object",
   "additionalProperties": false,
   "properties": {}
}

as explained here.

Now I want to validate attribute which

1. is of object type,
2. dont have any predefined properties
3. can have properties of type string or numeric
4. should not be empty

Enforcing non-emptyness (point 4) is what I am unable to guess. This is somewhat opposite of enforcing emptyness as in above example. My current json schema excerpt looks like this:

"attribute": 
{
    "type": "object",
    "additionalProperties": { "type": ["string","number","integer"] }
}

But above does not enforce non-emptyness. How can I accomplish this?

Answer 1

Sounds like minProperties is what you want.

{
    "type": "object",
    "additionalProperties": {"type": ["string", "number", "integer"]},
    "minProperties": 1
}

There is also maxProperties, which can be used as an alternative solution to the opposite question that you linked to.