1 unknow action
The action 'my_test' could not be found for MytestsController
在对应的MytestsController的控制器中找不到my_test这个方法，动作
2 Template is missing
找不到对应的视图，它会现找自己写的Controller对应的模板，如果找不到，
就会去找ApplicationController对应的模板，因为我们写的Controller继承了前者。
3 NoMethodError (You have anilobjectwhenyou didn't expect it!
You might have expected an instance ofArray.
The error occurredwhileevaluatingnil.each
调用方法的对象为空。这个是最常见的错误，根据错误信息可以知道，调用each方法的对象为空，只要检查each前的对象即可
nil.each
4 ActionController::RoutingError (No route matches
路径错误
5 ActionView::TemplateError (You have anilobjectwhenyou didn't expect it!
You might have expected an instance of ActiveRecord::Base.
The error occurredwhileevaluatingnil.[]) on line
与3类似，调用方法的对象为空
6 RuntimeError (Called idfornil, which would mistakenly be 4 --ifyou really wanted the id ofnil, use object_id):
find_by 必须要有查询不为空的结果，不然就报错。
7 ActionView::TemplateError (compile error
D:/cetcit/app/views/admin/data_stats/index.erb:30: syntax error, unexpected kENSURE, expecting kEND
D:/cetcit/app/views/admin/data_stats/index.erb:32: syntax error, unexpected$end, expecting kEND) on line#30 of app/views/admin/data_stats/index.erb:
使用循环语句或者控制语句时，忘记了end