Question

我无法将模型关联起来，或者我对如何通过关联进行查询无知。

class Entry < ActiveRecord::Base
  has_one :category
end

class Category < ActiveRecord::Base
  belongs_to :entry
end

现在，如果我进入我的rails控制台并询问Entry.first，我会得到：

Entry Load (0.1ms)  SELECT "entries".* FROM "entries" LIMIT 1
=> #<Entry id: 1, category_id: 1, duration: 2.0, image: "3", note: "4", url: "5", created_at: "2012-03-03 02:22:23", updated_at: "2012-03-03 02:22:23">

如果我问Category.first我得到：

Category Load (0.1ms)  SELECT "categories".* FROM "categories" LIMIT 1 
=> #<Category id: 1, name: "Dev", created_at: "2012-03-03 02:17:17", updated_at: "2012-03-03 02:17:17">

但是，如果我要求Entry.first.category.name，它会中断，我会：

Entry Load (0.1ms)  SELECT "entries".* FROM "entries" LIMIT 1
NoMethodError: undefined method `category' for #<Entry:0x007fec4d217848>
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/activemodel-3.2.1/lib/active_model/attribute_methods.rb:407:in `method_missing'
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/activerecord-3.2.1/lib/active_record/attribute_methods.rb:126:in `method_missing'
from (irb):63
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands/console.rb:47:in `start'
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands/console.rb:8:in `start'
from /Users/john/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands.rb:41:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'

这是为什么？如何通过条目获取该类别的名称？我做错了什么？

Answer 1

在您的情况下，类别表应包含entry_id列，但您在条目1中有category_id。

所以尝试改变：

class Entry < ActiveRecord::Base
  belongs_to :category
end

class Category < ActiveRecord::Base
  has_one :entry
end

或者更改数据库架构。

查询rails关联

1 个答案: