Fix migration to remove moved rows and post reference

Author: trichoplax

app/models/thread_follower.rb

@@ -1,15 +1,4 @@
 class ThreadFollower < ApplicationRecord
-  belongs_to :comment_thread, optional: true
-  belongs_to :post, optional: true
+  belongs_to :comment_thread
   belongs_to :user
-
-  validate :thread_or_post
-
-  private
-
-  def thread_or_post
-    if comment_thread.nil? && post.nil?
-      errors.add(:base, 'Must refer to either a comment thread or a post.')
-    end
-  end
 end

db/migrate/20251203164131_create_new_thread_followers.rb

@@ -12,19 +12,17 @@ def create_table_new_thread_followers
 
       t.timestamps
     end
-    add_index :new_thread_followers, :user_id
-    add_index :new_thread_followers, :post_id
+    add_index :new_thread_followers, [:user_id, :post_id]
   end
 
   def move_rows_with_non_nil_post_id
     NewThreadFollower.insert_all(
       ThreadFollower.select(:user_id, :post_id, :created_at, :updated_at).where.not(post_id:nil)
     )
+    ThreadFollower.where.not(post_id:nil).delete_all
   end
 
   def remove_post_id_column_from_thread_followers
-    change_table :thread_followers do |t|
-      t.remove :post_id
-    end
+    remove_reference :thread_followers, :post, index: true, foreign_key: true
   end
 end

db/schema.rb

@@ -406,8 +406,7 @@
     t.bigint "post_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.index ["post_id"], name: "index_new_thread_followers_on_post_id"
-    t.index ["user_id"], name: "index_new_thread_followers_on_user_id"
+    t.index ["user_id", "post_id"], name: "index_new_thread_followers_on_user_id_and_post_id"
   end
 
   create_table "notifications", charset: "utf8mb4", collation: "utf8mb4_unicode_ci", force: :cascade do |t|
@@ -732,9 +731,7 @@
     t.bigint "user_id"
     t.datetime "created_at", precision: nil, null: false
     t.datetime "updated_at", precision: nil, null: false
-    t.bigint "post_id"
     t.index ["comment_thread_id"], name: "index_thread_followers_on_comment_thread_id"
-    t.index ["post_id"], name: "index_thread_followers_on_post_id"
     t.index ["user_id"], name: "index_thread_followers_on_user_id"
   end
 
@@ -902,7 +899,6 @@
   add_foreign_key "tag_synonyms", "tags"
   add_foreign_key "tags", "communities"
   add_foreign_key "tags", "tags", column: "parent_id"
-  add_foreign_key "thread_followers", "posts"
   add_foreign_key "user_abilities", "abilities"
   add_foreign_key "user_abilities", "community_users"
   add_foreign_key "user_websites", "users"