rails + mysqlがpsqlになる

Question

OS: Ubuntu
OSバージョン: 18.04.2
rubyバージョン: 2.5.5
railsバージョン: Rails 5.2.3
mysqlバージョン： mysql Ver 14.14 Distrib 5.7.26, for Linux (x86_64) using EditLine wrapper

railsでmysqlを使うためにGemfileで以下のように記述し，

gem 'mysql2', '>= 0.4.4', '< 0.6.0'

そして，config/database.ymlを以下のように記述しました．

# MySQL. Versions 5.1.10 and up are supported.
#
# Install the MySQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   https://dev.mysql.com/doc/refman/5.7/en/password-hashing.html
#
default: &default
  adapter: mysql2
  encoding: utf8mb4
  charset: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: username
  password: password
  socket: /tmp/mysql.sock

development:
  <<: *default
  database: hoge_development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: hoge_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: hoge_production
  username: hoge
  password: <%= ENV['HOGE_APP_DATABASE_PASSWORD'] %>

そして，rails db:migrateをしたのですが，

rails aborted!
LoadError: Error loading the 'postgresql' Active Record adapter. Missing a gem it depends on? pg is not part of the bundle. Add it to your Gemfile.
/home/ubuntu/hoge_app/opinion_app/config/environment.rb:5:in `<top (required)>'
/home/ubuntu/hoge_app/opinion_app/bin/rails:9:in `<top (required)>'
/home/ubuntu/_app/opinion_app/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'

Caused by:
Gem::LoadError: pg is not part of the bundle. Add it to your Gemfile.
/home/ubuntu/hoge_app/opinion_app/config/environment.rb:5:in `<top (required)>'
/home/ubuntu/hoge_app/opinion_app/bin/rails:9:in `<top (required)>'
/home/ubuntu/hoge_app/opinion_app/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'
Tasks: TOP => db:migrate => db:load_config => environment
(See full trace by running task with --trace)

となぜかpsqlになってしまっています．どうすればよいでしょうか？
（なお，セキュリティのため,ここに買いてあるDATABASE名やusernameは適当に変更しています）

##試したこと
MacOSでは同じプログラムでmysqlで動いたので，プログラムに問題はないと思います．

Answer 1

ディレクトリを削除したりして，調べていたら，どうやらシェルの設定ファイル（私はfishなのでconfig.fish）にDATABASE_URLを書いていたのが原因でした．HOGE＿URLなどに名前を変更し，rails dbするとmysqlに接続できました．

#fish shellの場合です
#以下のようにしていたのが問題でした
set -x DATABASE_URL 'postgres://XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'

Answer 2

Gemfileに記述した後に、

bundle install

は行いましたでしょうか。

Comments

[退会済みユーザー]

はい，しています

[fshun]

- mysql は起動していますでしょうか

- mysql に database は作成されていますでしょうか
`rails db:create`

[退会済みユーザー]

- `sudo mysql -u root`でmysqlへのアクセスが確認できましたので，起動しています．

- `rails db:create`は以下のようにエラーが表示されできませんでした．
```
rails aborted!
LoadError: Error loading the 'postgresql' Active Record adapter. Missing a gem it depends on? pg is not part of the bundle. Add it to your Gemfile.
/home/ubuntu/twi_app/opinion_app/config/environment.rb:5:in `<top (required)>'
/home/ubuntu/twi_app/opinion_app/bin/rails:9:in `<top (required)>'
/home/ubuntu/twi_app/opinion_app/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'

Caused by:
Gem::LoadError: pg is not part of the bundle. Add it to your Gemfile.
/home/ubuntu/hoge_app/opinion_app/config/environment.rb:5:in `<top (required)>'
/home/ubuntu/hoge_app/opinion_app/bin/rails:9:in `<top (required)>'
/home/ubuntu/hoge_app/opinion_app/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'
Tasks: TOP => db:create => db:load_config => environment
(See full trace by running task with --trace)
```

[退会済みユーザー]

なお，Gemfileに`gem 'pg'`とすると，`rails db`したときにpsqlに接続されてしまいます

[fshun]

mysqlの起動確認ありがとうございます。
続けての質問、すみません。

Gemfileに `mysql2` 追加した際は、 `pg` は、削除されていますでしょうか。

また、Gemfileの中に `mysql2` を追加した後の、入力したコマンドなどを教えていただけないでしょうか。

[退会済みユーザー]

Gemfileの中身です
```
source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }
ruby '2.5.5'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.2.3'
# Use mysql as the database for Active Record
gem 'mysql2', '>= 0.4.4', '< 0.6.0'
#gem 'mysql2'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'mini_racer', platforms: :ruby

# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use ActiveStorage variant
# gem 'mini_magick', '~> 4.8'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.1.0', require: false

group :development, :test do
# Call 'byebug' anywhere in the code to stop execution and get a debugger console
gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
# Access an interactive console on exception pages or by calling 'console' anywhere in the code.
gem 'web-console', '>= 3.3.0'
gem 'listen', '>= 3.0.5', '< 3.2'
# Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
gem 'spring'
gem 'spring-watcher-listen', '~> 2.0.0'
end

group :test do
# Adds support for Capybara system testing and selenium driver
gem 'capybara', '>= 2.15'
gem 'selenium-webdriver'
# Easy installation and use of chromedriver to run system tests with Chrome
gem 'chromedriver-helper'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

gem 'omniauth'
gem 'omniauth-twitter'
gem 'bootstrap', '~> 4.3.1'
gem 'jquery-rails'
gem "attr_encrypted", "~> 3.1.0"
#gem 'pg'
```
>>>Gemfileに `mysql2` 追加した際は、 `pg` は、削除されていますでしょうか。
コメントアウトして，Gemfile.lockを削除して`sudo bundle install`をしてみましたが，結果は変わりませんでした．