chart.rb

class Chart < ApplicationRecord
  validate do |chart|
    schema = Rails.cache.fetch("vega_lite_schema/v5") do
      Faraday.get("https://vega.github.io/schema/vega-lite/v5.json").body
    end
    
    JsonSchemaValidator.new(chart, schema: schema, json: vega_json, field: :vega_json).validate
  end
end

json_schema_validator.rb

require "json_schemer"

class JsonSchemaValidator
  def initialize(record, schema:, json:, field:)
    @record = record
    @schema = schema
    @json = json
    @field = field
  end

  def validate
    schemer = JSONSchemer.schema(JSON.parse(@schema))

    @record.errors.add(@field, "Field #{@field} does not match JSON schema.") unless schemer.valid?(@json)
  end
end