Ruby-on-rails 获取 ActiveRecord::Relation 的未定义方法
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Getting undefined method for ActiveRecord::Relation
提问by Joseph Le Brech
I have the following models
我有以下型号
class Book < ActiveRecord::Base
has_many :chapters
end
and
和
class Chapter < ActiveRecord::Base
belongs_to :book
end
in /chapters/edit/idI get
在/chapters/edit/id我得到
undefined method `book' for #<ActiveRecord::Relation:0x0000010378d5d0>
when i try to access book like this
当我尝试访问这样的书时
@chapter.book
回答by alony
Looks like @chapter is not a single Chapter object. If @chapter is initialized something like this:
看起来@chapter 不是一个单独的 Chapter 对象。如果@chapter 被初始化是这样的：
@chapter = Chapter.where(:id => params[:id])
then you get a Relation object (that can be treated as a collection, but not a single object). So to fix this you need to retrieve a record using find_by_id, or take a first one from the collection
然后你会得到一个 Relation 对象（它可以被视为一个集合，但不是一个单一的对象）。因此，要解决此问题，您需要使用 检索记录find_by_id，或从集合中获取第一个记录
@chapter = Chapter.where(:id => params[:id]).first
or
或者
@chapter = Chapter.find_by_id(params[:id])
回答by Jason
As the others have said - adding the .firstmethod will resolve this. I have experienced this issue when calling a @chapter by it's unique ID. Adding .first(or .takein Rails 4) will ensure only one object is returned.
正如其他人所说 - 添加该.first方法将解决此问题。我在通过唯一 ID 调用 @chapter 时遇到过这个问题。添加.first（或.take在 Rails 4 中）将确保只返回一个对象。
回答by hellion
Try: Chapter.find(params[:id]).first
尝试： Chapter.find(params[:id]).first
