数据库类

NullDB Connection Adapter

https://github.com/nulldb/nulldb

当我们在本地执行RAILS_ENV=production rails assets:precompile编译资源时，会提示我们production数据库不存在，通过Gem activerecord-nulldb-adapter 可以避免创建数据库

Gemfile

gem 'activerecord-nulldb-adapter'

RAILS_ENV=production DATABASE_ADAPTER=nulldb rails assets:precompile

config/database.yml

default: &default
  adapter: <%= ENV.fetch('DATABASE_ADAPTER', 'postgresql') %>
  encoding: <%= ENV.fetch('DATABASE_ENCODING', 'unicode') %>
  # For details on connection pooling, see rails configuration guide
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  host: <%= ENV['DATABASE_HOST'] %>
  username: <%= ENV['DATABASE_USERNAME'] %>
  password: <%= ENV['DATABASE_PASSWORD'] %>
  port: <%= ENV['DATABASE_PORT'] %>
  timeout: 10