attributable.rb

module Attributable
  extend ActiveSupport::Concern

  included do
    has_many :attributions, as: :attributable
    has_many :sources, through: :attributions
  end
end

attribution.rb

# == Schema Information
#
# Table name: attributions
#
#  id                      :bigint(8)        not null, primary key
#  attributable_type       :string
#  attributable_id         :integer
#  source_id               :integer
#  user_id                 :integer
#  retrieved_on            :date
#  source_text             :text
#  description             :text
#  cross_issue             :boolean
#  cross_issue_description :text
#  created_at              :datetime         not null
#  updated_at              :datetime         not null
#

class Attribution < ApplicationRecord
  belongs_to :source
  belongs_to :attributable, polymorphic: true

  accepts_nested_attributes_for :source, reject_if: :all_blank, allow_destroy: true

  validates :source_id, presence: true
end

source.rb

# == Schema Information
#
# Table name: sources
#
#  id                 :bigint(8)        not null, primary key
#  name               :string
#  source_type        :string
#  url                :text
#  published_on       :date
#  marketable         :boolean
#  marketable_url     :text
#  marketable_details :text
#  created_at         :datetime         not null
#  updated_at         :datetime         not null
#  source_text        :text
#  authors            :text
#  catalog_number     :string
#

class Source < ApplicationRecord
  has_many :attributions

  validates :name,
            presence: true
end