gistfile1.txt

require 'dry-validation'
require 'rspec'

NestedSchema = Dry::Validation.JSON do
  key(:skus).each do
    optional(:cost).required(:decimal?)
    optional(:price).required(:decimal?)
    rule(price_or_cost: [:cost, :price]) do |cost, price|
      cost.filled? | price.filled?
    end
  end
end

FlatSchema = Dry::Validation.JSON do
  optional(:cost).required(:decimal?)
  optional(:price).required(:decimal?)
  rule(price_or_cost: [:cost, :price]) do |cost, price|
    cost.filled? | price.filled?
  end
end


RSpec.describe NestedSchema do
  it do
    expect(described_class.(skus: [{}]).messages).to_not be_empty
  end

  it do
    expect(described_class.(skus: [{price: 1}]).messages).to be_empty
  end

  it do
    expect(described_class.(skus: [{cost: 1}]).messages).to be_empty
  end
end

RSpec.describe FlatSchema do
  it do
    expect(described_class.({}).messages).to_not be_empty
  end

  it do
    expect(described_class.(price: 1).messages).to be_empty
  end

  it do
    expect(described_class.(cost: 1).messages).to be_empty
  end
end