nested_attributes in a one_to_many relationship with a presence validation on the parent model

nested_attributes_validation.rb

require 'sequel'
require 'sqlite3'
require 'logger'
require 'pry'

DB = Sequel.sqlite
DB.loggers << Logger.new($stdout)

Sequel::Model.plugin :validation_helpers

DB.instance_eval do
  create_table :products do
    primary_key :id
    String :name
    String :description
  end

  create_table :variants do
    primary_key :id
    String :name
    foreign_key :product_id, :products
  end
end

class Product < Sequel::Model
  one_to_many :variants

  plugin :nested_attributes
  nested_attributes :variants

   def variants_attributes=(variants)
    super
    associations[:variants].each{|v| v.skip_product_validation = true}
  end
end

class Variant < Sequel::Model
  many_to_one :product

  attr_accessor :skip_product_validation

  def validate
    super
    validates_presence :product unless skip_product_validation
  end
end

p = Product.new(name: 'bar', variants_attributes: [{ name: 'foo' }])
p.save

v = Variant.new(name: 'variant')
v.save

# binding.pry