有时候我们的rails应用并不需要操作数据库，一下子不知道怎么取消掉这个功能，最后在stackoverflow上找到了答案
If you are creating a new application, you can use -O to skip ActiveRecord:
rails new my_app -O
For existing applications:
1. Remove database adapter gems from your Gemfile (mysql2, sqlite3, etc.)
2. Change yourconfig/application.rb
Removerequire 'rails/allline and require frameworks you want to use, for example:
require "action_controller/railtie"
require "action_mailer/railtie"
require "sprockets/railtie"
require "rails/test_unit/railtie"
3. Delete yourdatabase.ymlfile,db/schema.rband migrations (if any)
4. Delete migration check intest/test_helper.rb
5. Delete any ActiveRecord configuration from yourconfig/environmentsfiles (this is what is causing your error)
This is all you need to do for an empty Rails app. If you run into problems caused by your existing code, stack trace should give you sufficient information on what you need to change. You might for example have some ActiveRecord configuration in your initializers.
