NameError: uninitialized constant モデル名　のエラー

前提・実現したいこと

<エラーが出るまでの背景>
deviseを利用したstudentモデルを削除するために
まずrails d model student
とし、その後
テーブルを削除するために
def change
drop_table :students
end
というメソッドを定義したマイグレーションファイル
を作成し、
それを実行するためにrails db:migrateとしたところエラーになりました。

そこで、
〇phpmyadminから直接studentsテーブルを削除
〇マイグレーションファイルを直接削除

し、その後もう一度studentモデルを作成するために
rails g devise student
としたところまたエラー文が出てしまいました。
※下記のエラー文はこの時のエラー文です

<開発環境>
awsのcloud9でrubyonrailsを利用してweleveという名前のwebアプリケーションを開発しています。
ターミナルの
ec2-user:~/environment/weleve (master) $
ディレクトリ下でコマンドを打っていました。

発生している問題・エラーメッセージ

/home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:80:in block in load_missing_constant': uninitialized constant Student (NameError) from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:9:in without_bootsnap_cache'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:80:in rescue in load_missing_constant' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/active_support.rb:59:in load_missing_constant'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/activesupport-5.2.4.1/lib/active_support/inflector/methods.rb:283:in const_get' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/activesupport-5.2.4.1/lib/active_support/inflector/methods.rb:283:in block in constantize'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/activesupport-5.2.4.1/lib/active_support/inflector/methods.rb:281:in each' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/activesupport-5.2.4.1/lib/active_support/inflector/methods.rb:281:in inject'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/activesupport-5.2.4.1/lib/active_support/inflector/methods.rb:281:in constantize' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise.rb:320:in get'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/mapping.rb:83:in to' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/mapping.rb:78:in modules'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/mapping.rb:95:in routes' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/mapping.rb:162:in default_used_route'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/mapping.rb:72:in initialize' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise.rb:350:in new'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise.rb:350:in add_mapping' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/rails/routes.rb:243:in block in devise_for'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/rails/routes.rb:242:in each' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/rails/routes.rb:242:in devise_for'
from /home/ec2-user/environment/weleve/config/routes.rb:2:in block in <top (required)>' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/actionpack-5.2.4.1/lib/action_dispatch/routing/route_set.rb:432:in instance_exec'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/actionpack-5.2.4.1/lib/action_dispatch/routing/route_set.rb:432:in eval_block' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/actionpack-5.2.4.1/lib/action_dispatch/routing/route_set.rb:414:in draw'
from /home/ec2-user/environment/weleve/config/routes.rb:1:in <top (required)>' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:55:in load'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:55:in load' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/routes_reloader.rb:41:in block in load_paths'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/routes_reloader.rb:41:in each' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/routes_reloader.rb:41:in load_paths'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/routes_reloader.rb:20:in reload!' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/routes_reloader.rb:30:in block in updater'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/activesupport-5.2.4.1/lib/active_support/file_update_checker.rb:83:in execute' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/routes_reloader.rb:10:in execute'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application/finisher.rb:130:in block in <module:Finisher>' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/initializable.rb:32:in instance_exec'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/initializable.rb:32:in run' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/initializable.rb:61:in block in run_initializers'
from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:228:in block in tsort_each' from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:350:in block (2 levels) in each_strongly_connected_component'
from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:431:in each_strongly_connected_component_from' from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:349:in block in each_strongly_connected_component'
from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:347:in each' from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:347:in call'
from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:347:in each_strongly_connected_component' from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:226:in tsort_each'
from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:205:in tsort_each' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/initializable.rb:60:in run_initializers'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/railties-5.2.4.1/lib/rails/application.rb:361:in initialize!' from /home/ec2-user/environment/weleve/config/environment.rb:5:in <top (required)>'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in require' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in block in require_with_bootsnap_lfi'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in register' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in require_with_bootsnap_lfi'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in require' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:106:in preload'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:157:in serve' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:145:in block in run'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:139:in loop' from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:139:in run'
from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application/boot.rb:19:in <top (required)>' from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:54:in require'
from /home/ec2-user/.rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:54:in require' from -e:1:in <main>'

該当のソースコード

試したこと

〇studentに関するマイグレーション(studentsテーブルを作成するためのマイグレーションファイルなど)を削除
〇rails db:migrate uninitialized constant
でググる
〇rails db:migrateと打つ
＝＞エラー発生
エラー文の最後に
Tasks: TOP => db:migrate => db:load_config => environment
(See full trace by running task with --trace)
と書いてあったが解釈できず、、

補足情報（FW/ツールのバージョンなど）

行動規範の内容に同意します

回答1件

ベストアンサー

エラーメッセージをweleveで検索し、貴方が書いたコードでのエラー発生箇所のみを見ると

from /home/ec2-user/.rvm/gems/ruby-2.5.1/gems/devise-4.7.1/lib/devise/rails/routes.rb:242:in devise_for'
from /home/ec2-user/environment/weleve/config/routes.rb:2:in block in <top (required)>'

あたりが浮かびあがります。

おそらく、config/routes.rbのdevise_forを消し忘れたせいで読み込めなくなっているのでしょう。

投稿2020/02/28 23:06