app/models/repost.rb
class Repost < ApplicationRecord
# Post that reposted.
belongs_to :post, foreign_key: :post_id,
class_name: 'Post', inverse_of: :repost
# Reposted post.
belongs_to :reposted, foreign_key: :reposted_id,
class_name: 'Post', inverse_of: :repost
belongs_to :user, inverse_of: :reposts
end