ransack で xxx_or_null を使って検索できるようにする

参考
+ https://github.com/activerecord-hackery/ransack/issues/123#issuecomment-247083120

config/initializers/ransack.rb

module Arel
  module Predications
    def eq_or_null(other)
      left  = eq(other)
      right = eq(nil)
      left.or(right)
    end

    def not_eq_or_null(other)
      left  = not_eq(other)
      right = eq(nil)
      left.or(right)
    end

    def gteq_or_null(other)
      left  = gteq(other)
      right = eq(nil)
      left.or(right)
    end

    def lt_or_null(other)
      left  = lt(other)
      right = eq(nil)
      left.or(right)
    end

    def in_or_null(other)
      left  = self.in(other)
      right = eq(nil)
      left.or(right)
    end
  end
end

Ransack.configure do |config|
  config.add_predicate 'eq_or_null', arel_predicate: 'eq_or_null'
  config.add_predicate 'not_eq_or_null', arel_predicate: 'not_eq_or_null'
  config.add_predicate 'gteq_or_null', arel_predicate: 'gteq_or_null'
  config.add_predicate 'lt_or_null', arel_predicate: 'lt_or_null'
  config.add_predicate 'in_or_null', arel_predicate: 'in_or_null', wants_array: true
end