覆盖database.yml的策略？

production:
  adapter: postgresql
  host: <%= ENV['DB_HOST'] %>
  username: <%= ENV['DB_USERNAME'] %>
  password: <%= ENV['DB_PASSWORD'] %>
  database: <%= ENV['DB_NAME'] %>

rails server -e production

<%=
  if Rails.env.production?
    {
      adapter: 'postgresql',
      host: 'production_host',
      username: 'production_username',
      password: 'production_password',
      database: 'production_database'
    }
  elsif Rails.env.staging?
    {
      adapter: 'postgresql',
      host: 'staging_host',
      username: 'staging_username',
      password: 'staging_password',
      database: 'staging_database'
    }
  else
    {
      adapter: 'postgresql',
      host: 'development_host',
      username: 'development_username',
      password: 'development_password',
      database: 'development_database'
    }
  end
%>

production:
  db_host: production_host
  db_username: production_username
  db_password: production_password
  db_name: production_database

production:
  adapter: postgresql
  host: <%= Rails.application.secrets.db_host %>
  username: <%= Rails.application.secrets.db_username %>
  password: <%= Rails.application.secrets.db_password %>
  database: <%= Rails.application.secrets.db_name %>