Rails 最近升级了 Rails 到 4.2.3，似乎发现了一个 Bug [已解决]
升级完后出现了个错误如下：
> undefined method `length' for nil:NilClass
app/views/api/messages/unread.json.jbuilder, line 1
- actionview (4.2.3) lib/action_view/helpers/cache_helper.rb:189:in `write_fragment_for'
- actionview (4.2.3) lib/action_view/helpers/cache_helper.rb:179:in `fragment_for'
- actionview (4.2.3) lib/action_view/helpers/cache_helper.rb:115:in `cache'
- app/views/api/messages/unread.json.jbuilder:1:in `_app_views_api_messages_unread_json_jbuilder___3570167334891618967_70131777006720'
- actionview (4.2.3) lib/action_view/template.rb:145:in `block in render'
经调查在 view 中使用 cache 的时候，不知为何 output_buffer 为 nil ，感觉不像是 Rails 的 Bug，可能是 Jbuilder 之类的原因，具体原因还未找到。
请大家也试试自己的应用，看是否有相同的问题。
# actionview-4.2.3/lib/action_view/helpers/cache_helper.rb#186
def write_fragment_for(name, options) #:nodoc:
# VIEW TODO: Make #capture usable outside of ERB
# This dance is needed because Builder can't use capture
pos = output_buffer.length
yield
output_safe = output_buffer.html_safe?
fragment = output_buffer.slice!(pos..-1)
if output_safe
self.output_buffer = output_buffer.class.new(output_buffer)
end
controller.write_fragment(name, fragment, options)
end
Update
这个问题排查了半天，回到升级前的版本一样出问题，经仔细比对代码，原来是我把 json.cache! 给误删成 cache 了！
真是脑残了，大家引以为戒~~
cache [:unread_messages, params[:version], current_user.id, current_user.unread_messages_received_at.value, @messages.limit_value, @messages.current_page] do
json.messages do
json.array! @messages, partial: 'api/messages/message', as: :message
end
json.current_page @messages.current_page
json.per_page @messages.limit_value
json.count @messages.total_count
end