访问has_one关联的属性 [英] Accessing a has_one associations' attributes
问题描述
我对Rails还是很陌生，所以希望这不是一个愚蠢的问题.
I'm still quite new to Rails so hopefully this isn't a silly question.
我有两个模型:User和Chore.用户has_one琐事，该杂事属于User
I have two models: User and Chore. User has_one chore, and Chore belongs to User
class User < ActiveRecord::Base
attr_accessible :chore_done, :email, :name, :phone
has_one :chore
class Chore < ActiveRecord::Base
attr_accessible :name, :user_id
belongs_to :user
在我的用户索引中，我试图显示所有用户并显示与他或她相关联的琐事.我这样做是通过将User.all传递到视图，并使用.each遍历每个用户:
In my user index, I'm trying to show all users and display the chore that is associated with him or her. I'm doing this by passing User.all to the view and using a .each to iterate through each user:
<% @users.each do |user| %>
<tr>
<td><%= user.name %></td>
<td><%= user.chore.name %></td>
<td><%= user.chore_done? %></td>
<td><%= link_to 'Edit', edit_user_path(user) %></td>
<td><%= link_to 'Destroy', user, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
不幸的是，我无法访问杂项的名称属性.我收到此错误:
Unfortunately, I cannot access the name attribute of the Chore. I get this error:
nil:NilClass的未定义方法名称"
undefined method `name' for nil:NilClass
如果删除.name属性，它将仅返回指向Chore对象的指针.
If I remove the .name attribute, it just returns a pointer to the Chore object.
我感觉这与将User.all对象传递给视图，然后对其进行迭代有关.只需在控制台中访问特定的User对象(例如User.find(1))，然后访问user.chore.name即可.
I have a feeling this has something to do with passing the User.all object to the view and then iterating over that. Just accessing a specific User object (e.g. User.find(1)) in the console, and then accessing user.chore.name works fine.
1.9.3-p194 :045 > user = User.find(4)
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", 4]]
=> #<User id: 4, name: "Example User", email: "example@dot.com", phone: 8675309, chore_done: false, created_at: "2012-11-05 01:53:33", updated_at: "2012-11-05 01:53:33">
1.9.3-p194 :046 > user.chore.name
Chore Load (0.3ms) SELECT "chores".* FROM "chores" WHERE "chores"."user_id" = 4 LIMIT 1
=> "Living room"
我在APIDock中阅读了一些有关AssociationProxy的内容，但是我认为我并不完全了解它，也不知道如何使用它.从我收集的数据来看，访问模型中的所有对象都会返回一个对象数组，但不会为其依赖项返回完整的属性集吗?因此，在这种情况下，我获得了指向Chore对象的指针，但无法访问其任何属性.
I read a bit about AssociationProxy in the APIDock, but I don't think I understand it completely nor do I know how to work with it. From what I gathered, accessing all objects in a model returns an Array of objects but doesn't return a complete set of attributes for its dependencies? So, in this case, I get a pointer to the Chore object but no access to any of its attributes.
我当然可以将Chore添加为用户表中的另一列，但将来可能会添加到该模型中+我只想弄清楚has_one关联的工作方式.
I could certainly just add Chore as another column in my user table, but I may add to that model in the future + I just want to figure out how the has_one association works anyway.
感谢您的帮助！
推荐答案
nil:NilClass的未定义方法名称"
undefined method `name' for nil:NilClass
这表示您正在尝试在Nil的实例上调用某些方法name().在您的代码上下文中，这表示此行上的chore是nil
This says that you are trying to call some method name() on an an instance of Nil. Within your code's context, that says that chore on this line is nil
<td><%= user.chore.name %></td>
简单地说，@user中的User实例之一没有关联的Chore.在您的视图中适应此问题的一种简单方法是检查user.chore是否存在.
Simply put, one of the User instances in @user has no associated Chore. One simple way to accomodate this in your view is by checking if user.chore exists.
<td><%= user.chore.nil? ? "some default name" : user.chore.name %></td>
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