Rails6 テーブル作成時のmigrateでエラーが出た話

目的

• テーブル作成を行なった際にmigrateでエラーが出た話をまとめる

エラー内容

• 下記コマンドでモデルファイルを作成した。

  $ rails g model user name:string
  

• その後、下記コマンドでmigreteを実行した。

  $ rails db:migrate
  

• 下記のエラーが発生した

  [14:50:10]MacBook-miriwo~/workspace/study/rails/tropical_fish_sns_of_rails$ rails db:migrate
  == 20200206055010 CreateUsers: migrating ======================================
  -- create_table(:users)
  rails aborted!
  StandardError: An error has occurred, all later migrations canceled:
  
  Mysql2::Error: Table 'users' already exists
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/db/migrate/20200206055010_create_users.rb:3:in `change'
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/bin/rails:9:in `<top (required)>'
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/bin/spring:15:in `<top (required)>'
  bin/rails:3:in `load'
  bin/rails:3:in `<main>'
  
  Caused by:
  ActiveRecord::StatementInvalid: Mysql2::Error: Table 'users' already exists
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/db/migrate/20200206055010_create_users.rb:3:in `change'
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/bin/rails:9:in `<top (required)>'
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/bin/spring:15:in `<top (required)>'
  bin/rails:3:in `load'
  bin/rails:3:in `<main>'
  
  Caused by:
  Mysql2::Error: Table 'users' already exists
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/db/migrate/20200206055010_create_users.rb:3:in `change'
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/bin/rails:9:in `<top (required)>'
  /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails/bin/spring:15:in `<top (required)>'
  bin/rails:3:in `load'
  bin/rails:3:in `<main>'
  Tasks: TOP => db:migrate
  (See full trace by running task with --trace)
  

原因調査

• 下記コマンドを実行して現在のmigrateのステータスを確認した。

  $ rails db:migrate:status
  

• 以前にmigrateを実施した際のmigrationファイルのが無いことが判明した。

  [14:52:57]MacBook- 
  miriwo~/workspace/study/rails/tropical_fish_sns_of_rails/db/migrate$ rails db:migrate:status
  
  database: tropical_fish_sns_development
  
   Status   Migration ID    Migration Name
  --------------------------------------------------
     up     20200206025324  ********** NO FILE **********
     up     20200206025916  ********** NO FILE **********
    down    20200206055010  Create users
  

解決法

• 下記コマンドを実行してDBのリセットを行なった。

  $ rails db:migrate:reset
  

• DBの状態を確認した。

  [14:54:33]MacBook-miriwo~/workspace/study/rails/tropical_fish_sns_of_rails/db/migrate$ rake 
  db:migrate:status
  (in /Users/admin/workspace/study/rails/tropical_fish_sns_of_rails)
  
  database: tropical_fish_sns_development
  
   Status   Migration ID    Migration Name
  --------------------------------------------------
     up     20200206055010  Create users
  

• 正常に反映されていることをがわかった。