#59

backend/app/models/post_similarity.rb

@@ -0,0 +1,4 @@
+class PostSimilarity < ApplicationRecord
+  belongs_to :post, class_name: 'Post', foreign_key: 'post_id'
+  belongs_to :target_post, class_name: 'Post', foreign_key: 'target_post_id'
+end

backend/db/migrate/20250729124200_create_post_similarities.rb

@@ -0,0 +1,9 @@
+class CreatePostSimilarities < ActiveRecord::Migration[7.0]
+  def change
+    create_table :post_similarities do |t|
+      t.references :post, null: false, foreign_key: { to_table: :posts }
+      t.references :target_post, null: false, foreign_key: { to_table: :posts }
+      t.float :cos, null: false
+    end
+  end
+end

backend/db/migrate/20250729210600_create_tag_similarities.rb

@@ -0,0 +1,9 @@
+class CreateTagSimilarities < ActiveRecord::Migration[7.0]
+  def change
+    create_table :tag_similarities do |t|
+      t.references :tag, null: false, foreign_key: { to_table: :tags }
+      t.references :target_tag, null: false, foreign_key: { to_table: :tags }
+      t.float :cos, null: false
+    end
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_06_29_140234) do
+ActiveRecord::Schema[8.0].define(version: 2025_07_29_210600) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -55,6 +55,14 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_29_140234) do
     t.index ["tag_id"], name: "index_nico_tag_relations_on_tag_id"
   end
 
+  create_table "post_similarities", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "post_id", null: false
+    t.bigint "target_post_id", null: false
+    t.float "cos", null: false
+    t.index ["post_id"], name: "index_post_similarities_on_post_id"
+    t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
+  end
+
   create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
@@ -97,6 +105,14 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_29_140234) do
     t.index ["tag_id"], name: "index_tag_aliases_on_tag_id"
   end
 
+  create_table "tag_similarities", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.bigint "target_tag_id", null: false
+    t.float "cos", null: false
+    t.index ["tag_id"], name: "index_tag_similarities_on_tag_id"
+    t.index ["target_tag_id"], name: "index_tag_similarities_on_target_tag_id"
+  end
+
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "category", default: "general", null: false
@@ -148,6 +164,8 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_29_140234) do
   add_foreign_key "active_storage_variant_records", "active_storage_blobs", column: "blob_id"
   add_foreign_key "nico_tag_relations", "tags"
   add_foreign_key "nico_tag_relations", "tags", column: "nico_tag_id"
+  add_foreign_key "post_similarities", "posts"
+  add_foreign_key "post_similarities", "posts", column: "target_post_id"
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
@@ -156,6 +174,8 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_29_140234) do
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
   add_foreign_key "tag_aliases", "tags"
+  add_foreign_key "tag_similarities", "tags"
+  add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
   add_foreign_key "user_ips", "ip_addresses"
   add_foreign_key "user_ips", "users"
   add_foreign_key "user_post_views", "posts"

backend/lib/tasks/calc_post_similarities.rake

@@ -0,0 +1,28 @@
+namespace :post_similarity do
+  desc '関聯投稿テーブル作成'
+  task calc: :environment do
+    dot = -> a, b { (a.keys & b.keys).sum { |k| a[k] * b[k] } }
+    norm = -> v { Math.sqrt(v.values.sum { |e| e * e }) }
+    cos = -> a, b do
+      na = norm.(a)
+      nb = norm.(b)
+      if na.zero? || nb.zero?
+        0.0
+      else
+        dot.(a, b) / na / nb
+      end
+    end
+
+    posts = Post.includes(:tags).to_a
+    posts.each_with_index do |post, i|
+      existence_of_tags = post.tags.index_with(1)
+      ((i + 1)...posts.size).each do |j|
+        target_post = posts[j]
+        existence_of_target_tags = target_post.tags.index_with(1)
+        PostSimilarity.find_or_initialize_by(post:, target_post:).tap { |ps|
+          ps.cos = cos.(existence_of_tags, existence_of_target_tags)
+        }.save!
+      end
+    end
+  end
+end