validation-rules.rb

require 'bundler/inline'

gemfile(true) do
  source 'https://rubygems.org'

  gem 'dry-validation'
end

schema = Dry::Validation.Schema do
  optional(:x).filled(:int?)
    .when(eql?: 1) { value(:y).filled? > value(:y2).filled? }
    .when(eql?: 1) { value(:y2).filled? > value(:y).filled? }
  optional(:y).filled(:int?)
  optional(:y2).filled(:int?)
  optional(:z).filled(:int?)
  rule(y_then_x: [:x, :y]) {|x, y| y.filled? > x.filled? }
  rule(z_then_x: [:x, :z]) {|x, z| z.filled? > x.filled? }
end

# success
p schema.({})
p schema.(x: 1)
p schema.(x: 1, y: 1, y2: 1)
p schema.(x: 1, z: 1)
p schema.(x: 0)
p schema.(x: 0, y: 1, z: 1)

# failure
p schema.(y: 1)
p schema.(z: 1)
p schema.(x: 1, y: 1)
p schema.(y: 1, z: 1)
p schema.(y: 1, y2: 1)
p schema.(x: 1, z: 1, y2: 1)

#<Dry::Validation::Result output={} errors={}>
#<Dry::Validation::Result output={:x=>1} errors={}>
#<Dry::Validation::Result output={:x=>1, :y=>1, :y2=>1} errors={}>
#<Dry::Validation::Result output={:x=>1, :z=>1} errors={}>
#<Dry::Validation::Result output={:x=>0} errors={}>
#<Dry::Validation::Result output={:x=>0, :y=>1, :z=>1} errors={}>
#<Dry::Validation::Result output={:y=>1} errors={:x_then_y=>["must be filled"]}>
#<Dry::Validation::Result output={:z=>1} errors={:x_then_z=>["must be filled"]}>
#<Dry::Validation::Result output={:x=>1, :y=>1} errors={:y2=>["must be filled"]}>
#<Dry::Validation::Result output={:y=>1, :z=>1} errors={:x_then_y=>["must be filled"], :x_then_z=>["must be filled"]}>
#<Dry::Validation::Result output={:y=>1, :y2=>1} errors={:x_then_y=>["must be filled"]}>
#<Dry::Validation::Result output={:x=>1, :z=>1, :y2=>1} errors={:y=>["must be filled"]}>