Conditional requirements with JSON Schema

As a JSON Schema user, I want to require certain properties based on the numeric value of another property.

An example case here is that I have a system where user can purchase a bus ticket (with value of 1) or a train ticket (with value of 2). If a train ticket is purchased, a seat must be included as tickets are tied to a specific seat but with bus, such requirement does not exist.

Bus ticket data

{
  "ticket_type": 1
}

Train ticket data

{
  "ticket_type": 2,
  "seat": 42
}

To validate this, our schema looks something like this:

{
  "$id": "https://example.com",
  "$schema": "https://json-schema.org/draft-04/schema",
  "type": "object",
  "properties": {
	  "ticket_type": { "type": "integer" },
	  "seat": { "type": "integer" }
  },
  "required": ["ticket_type"],
  "oneOf": [
    {
      "properties": { "ticket_type": { "const": 1 } }
    },
    {
	  "properties": { "ticket_type": { "const": 2 } },
	  "required": ["seat"]
    }
  ]
}

Here we define our two properties, ticket_type and seat. In oneOf restrictions, we require one of the two rules to match: either ticket_type equals 1 or ticket_type equals 2 AND seat is required.

If we want to instead do ranges (for example, require seat for any ticket_type that is larger than zero), we do:

{
  "$id": "https://example.com",
  "$schema": "https://json-schema.org/draft-04/schema",
  "type": "object",
  "properties": {
	  "ticket_type": { "type": "integer" },
	  "seat": { "type": "integer" }
  },
  "required": ["ticket_type"],
  "oneOf": [
    {
      "properties": { "ticket_type": { "const": 0 } }
    },
    {
	  "properties": { "ticket_type": { "minimum": 1 } },
	  "required": ["seat"]
    }
  ]
}