btrc-hub/backend/app/models/post_similarity.rb

class PostSimilarity < ApplicationRecord
  self.primary_key = :post_id, :target_post_id

  belongs_to :post, class_name: 'Post', foreign_key: 'post_id'
  belongs_to :target_post, class_name: 'Post', foreign_key: 'target_post_id'
end