ruby-on-rails - 为什么 Rails 找不到我在 Gemfile 中明确指定的 gem？

Question

我在 Rails 5.0.1 中使用 Ruby 2.4。我对为什么 Rails 说它找不到 gem 感到困惑。访问页面时出现此错误

Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).

但是，我已经在我的 Gemfile 中指定了它

gem 'pg'

这是我运行“bundle install”时的输出。你可以看到“pg”在那里。如何让 Rails 识别 gem？

localhost:scale nataliab$ bundle install
Your Gemfile lists the gem jquery-rails (>= 0) more than once.
You should probably keep only one of them.
While it's not a problem now, it could cause errors if you change the version of one of them later.
Using rake 12.3.0
Using concurrent-ruby 1.0.5
Using i18n 0.9.3
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.4
Using activesupport 5.0.6
Using builder 3.2.3
Using erubis 2.7.0
Using mini_portile2 2.3.0
Using nokogiri 1.8.1
Using rails-dom-testing 2.0.3
Using crass 1.0.3
Using loofah 2.1.1
Using rails-html-sanitizer 1.0.3
Using actionview 5.0.6
Using rack 2.0.3
Using rack-test 0.6.3
Using actionpack 5.0.6
Using nio4r 2.2.0
Using websocket-extensions 0.1.3
Using websocket-driver 0.6.5
Using actioncable 5.0.6
Using globalid 0.4.1
Using activejob 5.0.6
Using mini_mime 1.0.0
Using mail 2.7.0
Using actionmailer 5.0.6
Using activemodel 5.0.6
Using arel 7.1.4
Using activerecord 5.0.6
Using bindex 0.5.0
Using bundler 1.16.1
Using byebug 10.0.0
Using coffee-script-source 1.12.2
Using execjs 2.7.0
Using coffee-script 2.4.1
Using method_source 0.9.0
Using thor 0.20.0
Using railties 5.0.6
Using coffee-rails 4.2.2
Using multipart-post 2.0.0
Using faraday 0.12.2
Using ffi 1.9.18
Using hashie 3.5.7
Using multi_json 1.13.1
Using jbuilder 2.7.0
Using jquery-rails 4.3.1
Using jquery-ui-rails 6.0.1
Using jwt 1.5.6
Using rb-fsevent 0.10.2
Using rb-inotify 0.9.10
Using listen 3.0.8
Using multi_xml 0.6.0
Using oauth 0.5.4
Using oauth2 1.4.0
Using omniauth 1.8.1
Using omniauth-oauth2 1.3.1
Using omniauth-facebook 4.0.0
Using omniauth-google-oauth2 0.5.2
Using omniauth-linkedin-oauth2 0.2.5
Using omniauth-oauth 1.1.0
Using omniauth-twitter 1.4.0
Using pg 1.0.0
Using puma 3.11.2
Using sprockets 3.7.1
Using sprockets-rails 3.2.1
Using rails 5.0.6
Using rmagick 2.16.0
Using ruby-filemagic 0.7.2
Using sass-listen 4.0.0
Using sass 3.5.5
Using tilt 2.0.8
Using sass-rails 5.0.7
Using spring 2.0.2
Using spring-watcher-listen 2.0.1
Using sqlite3 1.3.13
Using turbolinks-source 5.1.0
Using turbolinks 5.1.0
Using uglifier 4.1.4
Using web-console 3.5.1
Bundle complete! 25 Gemfile dependencies, 81 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.

Answer 1

lock pg gem at 0.21.0 gem 'pg', '0.21.0' 因为 rails 还不支持 pg 在 1.0.0