对关联和从控制台获取信息感到困惑
Confusion over assocation and getting info from console
对尝试从 Rails 控制台获取信息感到困惑
我有以下型号：Article & Comment。
对于 Article，它是 has_many :comments
对于 Comment，它是 belongs_to :article
让我们假设它们是关联的，并且是有效的。顺便说一下。
架构如下：
ActiveRecord::Schema.define(version: 20160312052519) do
create_table "articles", force: :cascade do |t|
t.string "title"
t.text "text"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "comments", force: :cascade do |t|
t.string "commenter"
t.text "body"
t.integer "article_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "comments", ["article_id"], name: "index_comments_on_article_id"
end
这些是路线：
resources :articles do
resources :comments
end
当我 运行 命令如下：
Article.first.comments
Comment.first.article
Comment.first.article.title
Comment.first.article.text
Comment.first.commenter
Comment.first.body
它们都有效。
但是当我尝试 运行 在 Articles 上进行反向操作时，例如：
Article.first.comments.commenter
Article.first.comments.body
Article.all.comments
它们不起作用。为什么不？
编辑
这是我在 运行 Article.first.comments.commenter
时得到的
Article.first.comments.commenter
Article Load (23.0ms) SELECT "articles".* FROM "articles" ORDER BY "articles"."id" ASC LIMIT 1
NoMethodError: Comment Load (0.4ms) SELECT "comments".* FROM "comments" WHERE "comments"."article_id" = ? [["article_id", 1]]
undefined method `commenter' for #<Comment::ActiveRecord_Associations_CollectionProxy:0x007fa32b7e3d00>
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.2.5/lib/active_record/relation/delegation.rb:136:in `method_missing'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.2.5/lib/active_record/relation/delegation.rb:99:in `method_missing'
from (irb):127
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/console.rb:110:in `start'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/console.rb:9:in `start'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:68:in `console'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:274:in `require'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:274:in `block in require'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:240:in `load_dependency'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:274:in `require'
from /Users/aa/dropbox/beginningRails/guideblogagain/bin/rails:9:in `<top (required)>'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `block in load'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:240:in `load_dependency'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/commands/rails.rb:6:in `call'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/command_wrapper.rb:38:in `call'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:185:in `block in serve'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `fork'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `serve'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:131:in `block in run'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `loop'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `run'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application/boot.rb:18:in `<top (required)>'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
Article.first.comments是一个ActiveRecord_Associations_CollectionProxy对象，类似于数组。如果你想为每条评论获取评论者，你可以使用 map
Article.first.comments.map(&:commenter)
或者您可以获得第一条评论的评论者：
Article.first.comments.first.commenter
与以下内容相同：
Article.first.comments.body # Won't work
Article.first.comments.map(&:body) # Returns an array (each comment's body)
Article.all.comments # Won't work
Article.all.map(&:comments) # Returns an array (each article's comments)
当您 运行 您的工作示例 Article.first.comments 时，请查看实际的 return 值。你看到了什么？ return 是一个对象数组，对吧？所以说 Article.first 有 10 Comments。当你 运行 你的查询时，ActiveRecord 会 return 你一个包含 10 Comment 个对象的数组。
现在让我们看一下您的一个无效示例。
说，Article.first.comments.commenter。我们再次从 Article.first 开始，我们知道 return 是我们数据库中的第一个 Article 对象。
不过接下来要考虑Article.first.comments。
我们已经确信这是一个 Comment 对象数组，对吧？问题就在这里——commenter 是单个 Comment 对象的属性。
但是您没有一个 Comment 对象——您有一个 Comment 个对象的数组，并且 commenter 没有在数组上定义。
Article.first.comments.body 问题是一样的。这有意义吗？
您可以在控制台中执行以下操作：
Article.first.comments.each do |comment|
puts comment.commenter
end
然后您可以获得所有 commenter/body 值。
使用这种思路，我认为您将能够让自己相信 Article.all.comments 的问题，但如果没有，请随时发表评论，我们可以讨论。
Here are the docs为Active Record关系，供参考。干杯!
对尝试从 Rails 控制台获取信息感到困惑
我有以下型号：Article & Comment。
对于 Article，它是 has_many :comments
对于 Comment，它是 belongs_to :article
让我们假设它们是关联的，并且是有效的。顺便说一下。
架构如下：
ActiveRecord::Schema.define(version: 20160312052519) do
create_table "articles", force: :cascade do |t|
t.string "title"
t.text "text"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "comments", force: :cascade do |t|
t.string "commenter"
t.text "body"
t.integer "article_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "comments", ["article_id"], name: "index_comments_on_article_id"
end
这些是路线：
resources :articles do
resources :comments
end
当我 运行 命令如下：
Article.first.comments
Comment.first.article
Comment.first.article.title
Comment.first.article.text
Comment.first.commenter
Comment.first.body
它们都有效。
但是当我尝试 运行 在 Articles 上进行反向操作时，例如：
Article.first.comments.commenter
Article.first.comments.body
Article.all.comments
它们不起作用。为什么不？
编辑
这是我在 运行 Article.first.comments.commenter
Article.first.comments.commenter
Article Load (23.0ms) SELECT "articles".* FROM "articles" ORDER BY "articles"."id" ASC LIMIT 1
NoMethodError: Comment Load (0.4ms) SELECT "comments".* FROM "comments" WHERE "comments"."article_id" = ? [["article_id", 1]]
undefined method `commenter' for #<Comment::ActiveRecord_Associations_CollectionProxy:0x007fa32b7e3d00>
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.2.5/lib/active_record/relation/delegation.rb:136:in `method_missing'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activerecord-4.2.5/lib/active_record/relation/delegation.rb:99:in `method_missing'
from (irb):127
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/console.rb:110:in `start'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/console.rb:9:in `start'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:68:in `console'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:274:in `require'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:274:in `block in require'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:240:in `load_dependency'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:274:in `require'
from /Users/aa/dropbox/beginningRails/guideblogagain/bin/rails:9:in `<top (required)>'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `block in load'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:240:in `load_dependency'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/activesupport-4.2.5/lib/active_support/dependencies.rb:268:in `load'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/commands/rails.rb:6:in `call'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/command_wrapper.rb:38:in `call'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:185:in `block in serve'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `fork'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `serve'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:131:in `block in run'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `loop'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `run'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/spring-1.6.4/lib/spring/application/boot.rb:18:in `<top (required)>'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/aa/.rbenv/versions/2.1.4/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
Article.first.comments是一个ActiveRecord_Associations_CollectionProxy对象，类似于数组。如果你想为每条评论获取评论者，你可以使用 map
Article.first.comments.map(&:commenter)
或者您可以获得第一条评论的评论者：
Article.first.comments.first.commenter
与以下内容相同：
Article.first.comments.body # Won't work
Article.first.comments.map(&:body) # Returns an array (each comment's body)
Article.all.comments # Won't work
Article.all.map(&:comments) # Returns an array (each article's comments)
当您 运行 您的工作示例 Article.first.comments 时，请查看实际的 return 值。你看到了什么？ return 是一个对象数组，对吧？所以说 Article.first 有 10 Comments。当你 运行 你的查询时，ActiveRecord 会 return 你一个包含 10 Comment 个对象的数组。
现在让我们看一下您的一个无效示例。
说，Article.first.comments.commenter。我们再次从 Article.first 开始，我们知道 return 是我们数据库中的第一个 Article 对象。
不过接下来要考虑Article.first.comments。
我们已经确信这是一个 Comment 对象数组，对吧？问题就在这里——commenter 是单个 Comment 对象的属性。
但是您没有一个 Comment 对象——您有一个 Comment 个对象的数组，并且 commenter 没有在数组上定义。
Article.first.comments.body 问题是一样的。这有意义吗？
您可以在控制台中执行以下操作：
Article.first.comments.each do |comment|
puts comment.commenter
end
然后您可以获得所有 commenter/body 值。
使用这种思路，我认为您将能够让自己相信 Article.all.comments 的问题，但如果没有，请随时发表评论，我们可以讨论。
Here are the docs为Active Record关系，供参考。干杯!