acts-as-taggable-on導入時のエラー

Question

acts-as-taggable-onサイトを参考に導入し、次の順番に実行しました。

gem 'acts-as-taggable-on', '~> 6.0'

$ bundle install
$ rails acts_as_taggable_on_engine:install:migrations
$ rails db:migrate

上記最後のコマンドを実行した際、下記のエラーが発生してしましたまし。
パッと見何のエラーなのかはわかりますが、なぜ「起きたのか」と「対策」がわからない状態です。
ネットでも検索してみましたが、解決に至らずの状態です。。。
どなたか原因と対策が分かる方、ご教授お願い致します????‍♀️

== 20191121134718 ActsAsTaggableOnMigration: migrating ========================
-- create_table(:tags, {:options=>"ENGINE=InnoDB", :id=>:integer})
   -> 0.0398s
-- create_table(:taggings, {:options=>"ENGINE=InnoDB", :id=>:integer})
   -> 0.0564s
-- add_index(:taggings, :tag_id)
   -> 0.0630s
-- add_index(:taggings, [:taggable_id, :taggable_type, :context], {:name=>"taggings_taggable_context_idx"})
   -> 0.0484s
== 20191121134718 ActsAsTaggableOnMigration: migrated (0.2116s) ===============

== 20191121134719 AddMissingUniqueIndices: migrating ==========================
-- add_index(:tags, :name, {:unique=>true})
   -> 0.0736s
-- index_exists?(:taggings, :tag_id, {:name=>"index_taggings_on_tag_id"})
   -> 0.0120s
-- remove_index(:taggings, {:column=>:tag_id, :name=>"index_taggings_on_tag_id"})
rails aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Cannot drop index 'index_taggings_on_tag_id': needed in a foreign key constraint: DROP INDEX `index_taggings_on_tag_id` ON `taggings`
/usr/local/bundle/gems/mysql2-0.5.2/lib/mysql2/client.rb:131:in `_query'
/usr/local/bundle/gems/mysql2-0.5.2/lib/mysql2/client.rb:131:in `block in query'
/usr/local/bundle/gems/mysql2-0.5.2/lib/mysql2/client.rb:130:in `handle_interrupt'
/usr/local/bundle/gems/mysql2-0.5.2/lib/mysql2/client.rb:130:in `query'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:187:in `block (2 levels) in execute'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/dependencies/interlock.rb:48:in `block in permit_concurrent_loads'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/concurrency/share_lock.rb:187:in `yield_shares'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/dependencies/interlock.rb:47:in `permit_concurrent_loads'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:186:in `block in execute'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract_adapter.rb:581:in `block (2 levels) in log'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract_adapter.rb:580:in `block in log'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/notifications/instrumenter.rb:23:in `instrument'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract_adapter.rb:571:in `log'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:185:in `execute'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/mysql/database_statements.rb:28:in `execute'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/schema_statements.rb:788:in `remove_index'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:871:in `block in method_missing'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:840:in `block in say_with_time'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:840:in `say_with_time'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:860:in `method_missing'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration/compatibility.rb:184:in `remove_index'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:604:in `method_missing'
/idea-note/db/migrate/20191121134719_add_missing_unique_indices.acts_as_taggable_on_engine.rb:11:in `up'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:777:in `up'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:817:in `exec_migration'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:798:in `block (2 levels) in migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:797:in `block in migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:416:in `with_connection'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:796:in `migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:977:in `migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1292:in `block in execute_migration_in_transaction'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1345:in `ddl_transaction'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1291:in `execute_migration_in_transaction'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1263:in `block in migrate_without_lock'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1262:in `each'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1262:in `migrate_without_lock'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1210:in `block in migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1363:in `with_advisory_lock'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1210:in `migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1036:in `up'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/migration.rb:1011:in `migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/tasks/database_tasks.rb:172:in `migrate'
/usr/local/bundle/gems/activerecord-5.2.3/lib/active_record/railties/databases.rake:60:in `block (2 levels) in <main>'
/usr/local/bundle/gems/railties-5.2.3/lib/rails/commands/rake/rake_command.rb:23:in `block in perform'
/usr/local/bundle/gems/railties-5.2.3/lib/rails/commands/rake/rake_command.rb:20:in `perform'
/usr/local/bundle/gems/railties-5.2.3/lib/rails/command.rb:48:in `invoke'
/usr/local/bundle/gems/railties-5.2.3/lib/rails/commands.rb:18:in `<main>'
/usr/local/bundle/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
/usr/local/bundle/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
/usr/local/bundle/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
/usr/local/bundle/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
/usr/local/bundle/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
/usr/local/bundle/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
bin/rails:4:in `<main>'

Answer 1

僕も同じエラーに遭遇したので調べてみました。gemのバグだと思います。

原因は、db/migrate/20191130135317_acts_as_taggable_on_migration.acts_as_taggable_on_engine.rbの15行目で外部キーを設定しているにも関わらず、

t.references :tag, foreign_key: { to_table: ActsAsTaggableOn.tags_table }

db/migrate/20191130144523_add_missing_unique_indices.acts_as_taggable_on_engine.rbの11行目で外部キーを削除せずにインデックスを削除しようとしているからですね。

remove_index ActsAsTaggableOn.taggings_table, :tag_id if index_exists?(ActsAsTaggableOn.taggings_table, :tag_id)

インデックス削除前にこんな感じで外部キーを削除してあげれば想定通りの動きをしますが、コメントアウトでも変わらない気がします。ちゃんと発行されているSQLは確認していませんが。

if index_exists?(ActsAsTaggableOn.taggings_table, :tag_id)
  remove_foreign_key :taggings, :tags
  remove_index ActsAsTaggableOn.taggings_table, :tag_id
end

最初はRailsのバージョンアップなどでremove_indexの発行するSQLが変わったのかなーと思いましたが、CHANGELOGをパッと見た感じ見つかりませんでした。

参考になれば幸いです。

Comments

[isacRu]

やっぱりGemのバグですか
回答参考にさせていただきました。

ありがとうございます。

Answer 2

一応仮解決？

/idea-note/db/migrate/20191121134719_add_missing_unique_indices.acts_as_taggable_on_engine.rb

の１１行をコメントアウト、マイグレーションを実行したら、エラーは出ませんでした。
このGEMのバグでしょうかね？

おそらくそうだと思いますが、解釈が間違っていればご指摘お願いします????‍♀️