Heroku和Rails：Postgres的Gem加载错误，但它在GEMFILE中指定
所以我试图将一个小项目部署到Heroku，但是当我部署它并试图运行heroku run rake db:migrate它返回了我以下错误：
rake aborted! Gem::LoadError: 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). /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/connection_specification.rb:174:in `spec' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/connection_handling.rb:50:in `establish_connection' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/railtie.rb:120:in `block (2 levels) in ' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:28:in `block in on_load' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:27:in `each' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:27:in `on_load' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/railtie.rb:116:in `block in ' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `instance_exec' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `run' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:55:in `block in run_initializers' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:54:in `run_initializers' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:352:in `initialize!' /app/config/environment.rb:5:in `' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `block in require' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:240:in `load_dependency' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:328:in `require_environment!' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:457:in `block in run_tasks_blocks' Gem::LoadError: pg is not part of the bundle. Add it to Gemfile. /app/vendor/bundle/ruby/2.2.0/gems/bundler-1.11.2/lib/bundler/rubygems_integration.rb:304:in `block in replace_gem' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/postgresql_adapter.rb:16:in `' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `block in require' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:240:in `load_dependency' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/connection_adapters/connection_specification.rb:175:in `spec' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/connection_handling.rb:50:in `establish_connection' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/railtie.rb:120:in `block (2 levels) in ' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:28:in `block in on_load' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:27:in `each' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/lazy_load_hooks.rb:27:in `on_load' /app/vendor/bundle/ruby/2.2.0/gems/activerecord-4.2.6/lib/active_record/railtie.rb:116:in `block in ' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `instance_exec' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `run' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:55:in `block in run_initializers' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/initializable.rb:54:in `run_initializers' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:352:in `initialize!' /app/config/environment.rb:5:in `' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `block in require' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:240:in `load_dependency' /app/vendor/bundle/ruby/2.2.0/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:328:in `require_environment!' /app/vendor/bundle/ruby/2.2.0/gems/railties-4.2.6/lib/rails/application.rb:457:in `block in run_tasks_blocks' Tasks: TOP => db:migrate => environment (See full trace by running task with --trace)
我可以从第一行看到我需要在我的gem文件中加载pg gem，但是我已经将它加载到生产组中并通过bundle安装。 这是我的GEMFILE ：
source 'https://rubygems.org' # Bundle edge Rails instead: gem 'rails', github: 'rails/rails' gem 'rails', '4.2.6' gem 'sass-rails', '~> 5.0' gem 'uglifier', '>= 1.3.0' gem 'coffee-rails', '~> 4.1.0' gem 'jquery-rails' gem 'turbolinks' gem 'jbuilder', '~> 2.0' gem 'sdoc', '~> 0.4.0', group: :doc gem 'devise', '~> 3.5', '>= 3.5.6' gem 'paperclip', '~> 4.3', '>= 4.3.6' gem 'materialize-sass' gem "font-awesome-rails" gem 'bootstrap-sass', '~> 3.2.0' gem 'autoprefixer-rails' gem 'ratyrate' group :development, :test do gem 'byebug' end group :development do gem 'web-console', '~> 2.0' gem 'spring' end group :development do gem 'sqlite3' end group :production do gem 'pg' gem 'rails_12factor' end
在发布这个问题之前，我已经阅读了同一个问题的答案（ rake关于数据库适配器与database.yml不一致 ， rake中止了！Gem :: LoadError：为数据库适配器指定’postgresql’ ， Gem :: LoadError：指定’postgresql’为数据库适配器，但没有加载gem ）使用那里的答案，仍然发生错误。
谢谢你的帮助:)
尝试在生产之外编写pg，捆绑，使用gemlock，gemfile和push代码将代码提交到heroku，然后再试一次
我有这个问题并通过更改为：
'pg', '~> 0.20'