[Rails] What to do when the error No database selected and Unknown database appears in db: migrate

Introduction

I started creating web services today because I wanted to put the ideas I came up with into shape. Immediately, I was addicted to the error, so I will leave it as a memorandum.

environment


Rails : 6.0.3.2
ruby  : 2.6.3

error contents

I am creating a user login screen with devise. An error occurred with the following command.

Terminal


$ rake db:migrate

rake aborted!
ActiveRecord::StatementInvalid: Mysql2::Error: No database selected

Apparently, the database has not been selected. If you check database.yml, ...

database.yml


default: &default
   adapter: mysql2
   encoding: utf8
   pool: 5
   username: <%= ENV['DATABASE_DEV_USER'] %>
   password: <%= ENV['DATABASE_DEV_PASSWORD'] %>
   host: <%= ENV['DATABASE_DEV_HOST'] %>

development:
   <<: *default
   database: <%= ENV['DATABASE_DEV_NAME'] %>

test:
   <<: *default
   database: <%= ENV['DATABASE_DEV_NAME'] %>

production:
   <<: *default
   database: <%= ENV['DATABASE_DEV_NAME'] %>

database is specified by an environment variable, It seems that an error occurred because there is nothing in the .env file.

Write database in database.yml directly instead of environment variables.

database.yml


default: &default
   adapter: mysql2
   encoding: utf8
   pool: 5
   username: <%= ENV['DATABASE_DEV_USER'] %>
   password: <%= ENV['DATABASE_DEV_PASSWORD'] %>
   host: <%= ENV['DATABASE_DEV_HOST'] %>

development:
   <<: *default
   database: development

test:
   <<: *default
   database: test

production:
   <<: *default
   database: production

Run rake db: migrate again.

Terminal


rake aborted!
ActiveRecord::NoDatabaseError: Unknown database 'development'

Is displayed. Apparently the database cannot be found.

Create database with rails & migrate (MySQL) I referred to the above article.

###Database creation
rake db:create:all

###migration
rake db:migrate

This completes successfully.

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