Add 'or' and 'and_not' methods to AR::Relation

scope_operators_initializer.rb

module ScopeOperators
  def or(other).
    left = arel.constraints.reduce(:and)
    right = other.arel.constraints.reduce(:and)
    scope = merge(other)
    left ||= Arel::Nodes::Grouping.new(0) # take none if no conditions
    right ||= Arel::Nodes::Grouping.new(0) # take none if no conditions
    scope.where_values = [ Arel::Nodes::Grouping.new(left).or(Arel::Nodes::Grouping.new(right)) ]
    scope
  end 
  alias_method :|, :or

  def and_not(other)
    left = arel.constraints.reduce(:and)
    right = other.arel.constraints.reduce(:and)
    scope = merge(other)
    right ||= Arel::Nodes::Grouping.new('1=1') # take all if no conditions
    scope.where_values = [left, right.not].compact # to reject nil -> when there were no values
    scope
  end
end

ActiveSupport.on_load :active_record do 
  ActiveRecord::Relation.send(:include, ScopeOperators)
end