Rails教程第2章第2.3.3节

Question

我在2.3.3节中打开rails控制台。然后，我可以使用以下方法检索first_user

first_user = User.first

但是下一个命令有一个错误：

first_user.microposts

控制台消息：

> first_user.microposts
Micropost Load (0.4ms)  SELECT "microposts".* FROM "microposts" WHERE "microposts"."user_id" = 1
    ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: microposts.user_id: SELECT "microposts".* FROM "microposts"  WHERE "microposts"."user_id" = 1
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `initialize'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `new'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/sqlite3-1.3.5/lib/sqlite3/database.rb:91:in `prepare'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/sqlite_adapter.rb:246:in `block in exec_query'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activesupport-3.2.13/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/sqlite_adapter.rb:242:in `exec_query'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/sqlite_adapter.rb:467:in `select'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract/database_statements.rb:18:in `select_all'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/querying.rb:38:in `block in find_by_sql'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/explain.rb:41:in `logging_query_plan'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/querying.rb:37:in `find_by_sql'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/relation.rb:171:in `exec_queries'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/relation.rb:160:in `block in to_a'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/explain.rb:34:in `logging_query_plan'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/relation.rb:159:in `to_a'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/relation/finder_methods.rb:159:in `all'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/associations/collection_association.rb:382:in `find_target'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/associations/collection_association.rb:335:in `load_target'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/associations/collection_proxy.rb:44:in `load_target'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/activerecord-3.2.13/lib/active_record/associations/collection_proxy.rb:87:in `method_missing'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/railties-3.2.13/lib/rails/commands/console.rb:47:in `start'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/railties-3.2.13/lib/rails/commands/console.rb:8:in `start'
        from /Users/ryentzer/.rvm/gems/ruby-1.9.3-p429@rails3tutorial2ndEd/gems/railties-3.2.13/lib/rails/commands.rb:41:in `<top (required)>'
        from script/rails:6:in `require'
        from script/rails:6:in `<main>'

以下是我认为正在发生的事情。我最初通过添加、更新和删除用户和帖子来测试用户和Micropost。所以我认为微博不再与第一个用户联系在一起。

但是，我不知道如何看哪一个user_id是与微博相关的。

我目前有一个微博：

> Micropost.all
Micropost Load (0.3ms)  SELECT "microposts".* FROM "microposts" => [#<Micropost id: 4, content: "Testing", created_at: "2013-06-10 01:24:34", updated_at: "2013-06-10 01:24:34">] 

我如何知道哪个user_id与微柱相连？

Answer 1

问题是您的Micropost模型没有名为user_id的列。查看来自Micropost.all的控制台输出-在返回的名为user_id的实例中没有属性。也许你忘了迁移？也许你回过头了？也许你完全失足了一步？当您生成脚手架时，可能忘记了有关用户的部分。

玩这个应用程序(添加，删除，编辑)不会引起你的问题。当您再次检索第一个用户，并要求查看他们的错误信息时，如果一切都已正确设置，您将得到一些东西--至少是一个空的关系。

Answer 2

看看您的错误消息和来自Micropost.all的输出，我认为您需要向您的microposts表中添加一个名为user_id的新列。通过这种方式，Active Record可以通过使用micropost列来知道user所属的user_id。在设置了user_id模型和microposts模型之间的关系之后，可能忘记编写或运行迁移来将User列添加到Micropost表中。您可以阅读本指南以了解有关活动记录关联的更多信息。