我的rails项目之前有效。我收到此错误是因为我删除了mysql以及与mysql相关的所有内容。
然后我重新安装了mysql。它有这个错误。然后我重新安装了红宝石和铁轨。错误仍然存在。使用“rails new myapp”， 然后“捆绑安装”， 然后“rails s”，
我收到以下错误：
=> Booting WEBrick
=> Rails 4.0.2 application starting in development on
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
**/home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/railtie/configuration.rb:95:in `method_missing': undefined method `active_record' for #<Rails::Application::Configuration:0x0000000303cae8> (NoMethodError)
from /home/cwu/Dropbox/project/web/atop/config/environments/development.rb:23:in `block in <top (required)>'**
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/railtie/configurable.rb:24:in `class_eval'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/railtie/configurable.rb:24:in `configure'
from /home/cwu/Dropbox/project/web/atop/config/environments/development.rb:1:in `<top (required)>'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `require'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `block in require'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:214:in `load_dependency'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `require'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/engine.rb:591:in `block (2 levels) in <class:Engine>'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/engine.rb:590:in `each'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/engine.rb:590:in `block in <class:Engine>'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/initializable.rb:30:in `instance_exec'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/initializable.rb:30:in `run'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/initializable.rb:55:in `block in run_initializers'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:226:in `block in tsort_each'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:348:in `block (2 levels) in each_strongly_connected_component'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:418:in `block (2 levels) in each_strongly_connected_component_from'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:427:in `each_strongly_connected_component_from'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:417:in `block in each_strongly_connected_component_from'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/initializable.rb:44:in `each'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/initializable.rb:44:in `tsort_each_child'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:411:in `call'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:411:in `each_strongly_connected_component_from'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:347:in `block in each_strongly_connected_component'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:345:in `each'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:345:in `call'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:345:in `each_strongly_connected_component'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:224:in `tsort_each'
from /home/cwu/.rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/tsort.rb:205:in `tsort_each'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/initializable.rb:54:in `run_initializers'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/application.rb:215:in `initialize!'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /home/cwu/Dropbox/project/web/atop/config/environment.rb:5:in `<top (required)>'
from /home/cwu/Dropbox/project/web/atop/config.ru:3:in `require'
from /home/cwu/Dropbox/project/web/atop/config.ru:3:in `block in <main>'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/builder.rb:55:in `instance_eval'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/builder.rb:55:in `initialize'
from /home/cwu/Dropbox/project/web/atop/config.ru:in `new'
from /home/cwu/Dropbox/project/web/atop/config.ru:in `<main>'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/builder.rb:49:in `eval'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/builder.rb:49:in `new_from_string'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/builder.rb:40:in `parse_file'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/server.rb:277:in `build_app_and_options_from_config'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/server.rb:199:in `app'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands/server.rb:48:in `app'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/rack-1.5.2/lib/rack/server.rb:314:in `wrapped_app'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands/server.rb:75:in `start'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands.rb:76:in `block in <top (required)>'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands.rb:71:in `tap'
from /home/cwu/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands.rb:71:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'
答案 0 :(得分：8)
错误很明显，在config/environments/development.rb:23中配置了未加载的active_record。
只需删除
config.active_record.migration_error = :page_load
没问题。
答案 1 :(得分：2)
Leedy Liu在某种程度上是正确的，但如果您在创建新的Rails应用时遇到此错误，则表明您的环境存在更深层次的问题
根据this answer，您可能会在require "active_record/railtie"文件中注明application.rb。请检查以确保不是这种情况
您可能需要使用Rails重新安装ActiveRecord，以确保使用您的应用恢复功能。你试过这个：
gem install bundler
gem install rails
bundle install
除此之外，您需要确保正确安装Ruby on Rails。你在跑什么？ Linux还是Windows？
答案 2 :(得分：2)
作为一般修复，删除对active_record的所有引用。最简单的方法是在“active_records”的根目录上查找，查找所有用法，然后删除它们。我在config / application.rb和config / environments / development和production.rb。
中找到了用法答案 3 :(得分：0)
尝试：
'gem install bundler'
然后： ＆＃39;捆绑安装＆＃39; 试。
看看它是否清除。
答案 4 :(得分：0)
config.active_record.raise_in_transactional_callbacks = true中的config/application.rb和config.active_record.migration_error = :page_load中的config/environments/development.rb。