在引擎上运行` `rails generate`时，如何修复` `undefined method ` `railtie_namespace'`错误

Question

问题如下：

# 1) Create full engine `myengine` with Rails 4.2.10
rails _4.2.10_ plugin new myengine --full

# 2) Try to rails generate 
$ bin/rails g
/usr/local/lib/ruby/gems/2.6.0/gems/railties-4.2.10/lib/rails/engine/commands.rb:17:in `<top (required)>': 
  undefined method `railtie_namespace' for nil:NilClass (NoMethodError)

Answer 1

当您对引擎目录进行符号链接并通过如下链接到达该目录时，就会出现问题：

cd path/to/somewhere
rails _4.2.10_ plugin new myengine --full
ln -s path/to/somewhere/myengine ~/favorite/myengine

cd ~/favorite/myengine

./bin/rails g

如果你这样做了，你就会遇到错误。要解决此问题，请更改bin/rails顶部的某些行，如下所示：

# from 
ENGINE_ROOT = File.expand_path('../..', __FILE__)
ENGINE_PATH = File.expand_path('../../lib/myengine/engine', __FILE__)

# to
require 'pathname'
ENGINE_ROOT = Pathname.new(__FILE__).realpath + '../..'
ENGINE_PATH = ENGINE_ROOT + 'lib/myengine/engine'

请参阅::Rails::Engine.find的实现，了解补丁的工作原理。