多个 Rails 项目，每个项目都有不同的数据库

Question

我是 Rails 新手，在学习完 Heroku 教程后，我使用 PostgresQL 建立了一个项目。

一位也在学习 Rails 的朋友遵循了一个不同的教程，该教程使用 SQLite 作为数据库，我已经克隆了该教程。

使用 SQLite 项目启动 Rails 服务器时，我不断收到错误消息，提示该项目正在尝试使用 PostgresQL，并告诉我将 gem pg 添加到我的 Gemfile。

我似乎只能在网上找到各种关于从 MySQL/SQLite/etc 迁移到 PostgresQL 的帖子，但我不打算迁移。

我的database.yml如下：

# SQLite version 3.x
#   gem install sqlite3
#
#   Ensure the SQLite 3 gem is defined in your Gemfile
#   gem 'sqlite3'
#
default: &default
  adapter: sqlite3
  pool: 5
  timeout: 5000

development:
  <<: *default
  database: db/development.sqlite3

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: db/test.sqlite3

production:
  <<: *default
  database: db/production.sqlite3

RubyMine 报错是：

/usr/bin/ruby -e $stdout.sync=true;$stderr.sync=true;load($0=ARGV.shift) /Users/Ty/Rails/TSCLunch/web/bin/rails server -b 0.0.0.0 -p 3000 -e development
=> Booting WEBrick
=> Rails 4.2.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/Users/Ty/.gem/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec': 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). (Gem::LoadError)
    from /Users/Ty/.gem/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/connection_specification.rb:174:in `spec'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/connection_handling.rb:50:in `establish_connection'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/railtie.rb:120:in `block (2 levels) in <class:Railtie>'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:28:in `block in on_load'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:27:in `each'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:27:in `on_load'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/railtie.rb:116:in `block in <class:Railtie>'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:30:in `instance_exec'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:30:in `run'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:55:in `block in run_initializers'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:150:in `block in tsort_each'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:183:in `block (2 levels) in each_strongly_connected_component'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:219:in `each_strongly_connected_component_from'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:182:in `block in each_strongly_connected_component'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:180:in `each'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:180:in `each_strongly_connected_component'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:148:in `tsort_each'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:54:in `run_initializers'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/application.rb:352:in `initialize!'
    from /Users/Ty/Rails/TSCLunch/web/config/environment.rb:5:in `<top (required)>'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:in `require'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:in `block in require'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /Users/Ty/.gem/ruby/2.0.0/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:in `require'
    from /Users/Ty/Rails/TSCLunch/web/config.ru:3:in `block in <main>'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:55:in `instance_eval'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:55:in `initialize'
    from /Users/Ty/Rails/TSCLunch/web/config.ru:in `new'
    from /Users/Ty/Rails/TSCLunch/web/config.ru:in `<main>'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:49:in `eval'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:49:in `new_from_string'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:40:in `parse_file'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/server.rb:299:in `build_app_and_options_from_config'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/server.rb:208:in `app'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/server.rb:61:in `app'
    from /Users/Ty/.gem/ruby/2.0.0/gems/rack-1.6.0/lib/rack/server.rb:336:in `wrapped_app'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/server.rb:139:in `log_to_stdout'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/server.rb:78:in `start'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:80:in `block in server'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in `tap'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in `server'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
    from /Users/Ty/.gem/ruby/2.0.0/gems/railties-4.2.0/lib/rails/commands.rb:17:in `<top (required)>'
    from /Users/Ty/Rails/TSCLunch/web/bin/rails:4:in `require'
    from /Users/Ty/Rails/TSCLunch/web/bin/rails:4:in `<top (required)>'
    from -e:1:in `load'
    from -e:1:in `<main>'

Process finished with exit code 1

Answer 1

我假设你只是想获得一个在本地“工作”而不是在 heroku 上的项目，不管它是使用 Postgres 还是 SQLITE3，是吗？

您也可以发布您的 Gemfile 的副本吗？由于您遵循 Heroku 教程，因此从您的帖子中不清楚您遵循了哪些其他步骤，除了您可能通过在命令行上运行它来创建您的应用程序：

$> rails new myapp --database=postgresql

这会将“gem 'pg'”添加到您的 Gemfile 中，并为它创建一个适当的 database.yml。但是如果你复制了另一个指定 SQLITE3 的 database.yml，现在你的 Rails 环境就会混乱。

如果您的 Gemfile 中有“gem pg”，请尝试以下步骤：

1) 在您的 Gemfile 中，删除“pg”行并将其替换为： 宝石'sqlite3'

2) 执行“捆绑安装”以安装您克隆的 database.yml 指定的 SQLITE3。

3) 运行以下命令来重置您的数据库： $> rake db: 重置

希望这会让你再次前进。现在您应该有一个使用 SQLITE3 而不是 Postgres 的项目。您将无法将其部署到 Heroku，因为它们不允许 SQLITE3 用于生产。

如果你让它在本地使用 SQLITE3 工作，然后想部署到 Heroku，他们在这里提供了一个从 SQLITE3 移回 Postgres 的简单过程：https://devcenter.heroku.com/articles/sqlite3

Answer 2

您可以通过两种方式为 ActiveRecord 指定适配器。

1. 使用ENV['DATABASE_URL']环境变量
2. 使用database.yml配置文件

如果您同时设置了 config/database.yml 和 ENV['DATABASE_URL']，那么 Rails 会将配置合并在一起。我认为这是导致您的问题的原因。

如果是这样，您可以删除您的环境变量或在 database.yml 中明确指定 url

我鼓励您阅读以下文章以获取更多信息：http://guides.rubyonrails.org/configuring.html#configuring-a-database