Rails环境配置：“方法_缺失”：未定义方法`action_mailer‘

Question

试图调用Rails控制台(bundle exec rails c)或Rails服务器(bundle exec rails s)将引发以下异常：

~/project/.bundle/gems/railties-4.2.6/lib/rails/railtie/configuration.rb:95:in `method_missing': undefined method `action_mailer' for #<Rails::Application::Configuration:0x007fdbe46e7400> (NoMethodError)
    from ~/project/config/environments/development.rb:43:in `block in <top (required)>'
    from ~/project/.bundle/gems/railties-4.2.6/lib/rails/railtie.rb:210:in `instance_eval'
    from ~/project/.bundle/gems/railties-4.2.6/lib/rails/railtie.rb:210:in `configure'
    from ~/project/config/environments/development.rb:1:in `<top (required)>'
    from ~/project/.bundle/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require'
...

我是不是在这里或那里遗漏了一些可能导致不兼容问题的其他宝石？

这是config/environments/development.rb中的冒犯行

  # Save emails to files instead of delivering.
  config.action_mailer.delivery_method = :file

以下是我的Gemfile的内容：

source 'https://rubygems.org'

gem 'rails', '4.2.6'
gem 'activemodel'
gem 'actionmailer'
gem 'sass-rails', '~> 5.0.0'
gem 'uglifier', '>= 1.3.0'
gem 'rollbar'
gem 'meta-tags'
gem 'faraday'
gem 'oj'
gem 'dalli-elasticache'
gem 'config'

# Frontend
gem 'jquery-rails'
gem 'jquery-turbolinks'
gem 'bourbon'
gem 'turbolinks'
gem 'therubyracer'

# Deploy
gem 'capistrano'
gem 'capistrano-rbenv'
gem 'capistrano-bundler'
gem 'capistrano-rails'
gem 'capistrano-passenger'
gem 'capistrano-rails-console'
gem 'capistrano-rails-log'

group :development, :test do
  gem 'spring'
  gem 'spring-commands-rspec'
  gem 'byebug'
end

group :test do
  gem 'rspec-rails'
  gem 'capybara'
  gem 'launchy'
  gem 'webmock'
  gem 'capybara-webkit'
  gem 'vcr'
end

group :development do
  gem 'web-console', '~> 2.0'
  gem 'quiet_assets'
end

Answer 1

解决办法是增加：

require 'action_mailer/railtie'

到config/application.rb，因为该文件没有执行require 'rails/all。

Answer 2

我不能评论，所以我回答这里--我在Dockerfile中添加了下面的Docker容器中的这个错误，所以它对我是有效的，RUN BUNDLE_GEMFILE=Gemfile

Answer 3

在将Rails 5.2迁移到Rails 6.1期间，我遇到了同样的问题。问题是我安装了不同版本的“铁路”创业板。

因此，为了解决这个问题，在我将gem 'rails'版本升级为6.1之后，也将gem 'railties'升级为6.1。