已解决：这个问题是如何神秘消失的，这是 heroku 生成的 url
http://pacific-escarpment-9949.herokuapp.com/
如果有人能详细说明为什么它在 30 分钟前给出了错误页面，我将不胜感激，但现在不再如此。
它在本地运行良好。但是当我将它推送到 Heroku 时，它给出了这个错误。
我认为它与数据库有关，因为我使用了以下命令：
rails generate migration add_user_id_to_post integer (pseudocode, it worked fine)
我已经运行：$ heroku run rake db:migrate
应该是主页的页面显示：我们很抱歉，但出了点问题。
我之前遇到过这个问题，但是当我运行 heroku run rake db:migrate 时，它解决了这个问题。但这次不是。请帮助。我已经被困了3个小时了。谢谢你。
这是我在 git hub 上的仓库：https ://github.com/nixor/blog
请原谅我的菜鸟，所有这些对我来说都是 2 周新的。
nixor@unix:$ heroku run rake db:migrate
Running `rake db:migrate` attached to terminal... up, run.1
DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from <top (required)> at /app/Rakefile:7)
DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from <top (required)> at /app/Rakefile:7)
Connecting to database specified by DATABASE_URL
Migrating to CreatePosts (20121124111726)
== CreatePosts: migrating ====================================================
-- create_table(:posts)
NOTICE: CREATE TABLE will create implicit sequence "posts_id_seq" for serial column "posts.id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "posts_pkey" for table "posts"
-> 0.0215s
== CreatePosts: migrated (0.0216s) ===========================================
Migrating to CreateUsers (20121126134513)
== CreateUsers: migrating ====================================================
-- create_table(:users)
NOTICE: CREATE TABLE will create implicit sequence "users_id_seq" for serial column "users.id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "users_pkey" for table "users"
-> 0.0121s
== CreateUsers: migrated (0.0122s) ===========================================
Migrating to AddUserIdToPosts (20121126173652)
== AddUserIdToPosts: migrating ===============================================
-- add_column(:posts, :user_id, :integer)
rake aborted!
An error has occurred, this and all later migrations canceled:
PGError: ERROR: column "user_id" of relation "posts" already exists
: ALTER TABLE "posts" ADD COLUMN "user_id" integer
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/postgresql_adapter.rb:652:in `async_exec'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/postgresql_adapter.rb:652:in `block in execute'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log'
/app/vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.9/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/postgresql_adapter.rb:651:in `execute'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/postgresql_adapter.rb:1025:in `add_column'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:466:in `block in method_missing'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:438:in `block in say_with_time'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:438:in `say_with_time'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:458:in `method_missing'
/app/db/migrate/20121126173652_add_user_id_to_posts.rb:3:in `change'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:407:in `block (2 levels) in migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:407:in `block in migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract/connection_pool.rb:129:in `with_connection'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:389:in `migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:528:in `migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:720:in `block (2 levels) in migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:775:in `call'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:775:in `block in ddl_transaction'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/transactions.rb:208:in `transaction'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:775:in `ddl_transaction'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:719:in `block in migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:700:in `each'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:700:in `migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:570:in `up'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/migration.rb:551:in `migrate'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.9/lib/active_record/railties/databases.rake:179:in `block (2 levels) in <top (required)>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)