我在这里做一些明显错误的事情，但我不明白。
我有一个像这样的部分调用：
= render 'shared/purchase', collection: @purchases
@purchases在控制器中定义如下：
@purchases = current_user.purchases
但我得到这个错误：
app/views/shared/_purchase.html.slim where line #3 raised:
undefined local variable or method `purchase' for #<<Class:0x007fd8ca54f970>:0x007fd8ca54eb60>
但是，当我将部分更改为仅渲染 local_assigns 时，我看到了：
[:collection, #<ActiveRecord::Associations::CollectionProxy [#<Purchase id: 40, user_id: 20, purchaseable_id: 6, purchaseable_type: "PurchaseType", frequency: "Weekly", day: "Su", notes: "leave at gate", allergies: "peanuts", created_at: "2013-07-24 16:58:08", updated_at: "2013-07-24 16:58:08", size: "Normal", quantity: 2>, #<Purchase id: 41, user_id: 20, purchaseable_id: 5, purchaseable_type: "PurchaseType", frequency: "Weekly", day: "Su", notes: "leave at gate", allergies: "peanuts", created_at: "2013-07-24 16:58:08", updated_at: "2013-07-24 16:58:08", size: "Jumbo", quantity: 3>, #<Purchase id: 42, user_id: 20, purchaseable_id: 7, purchaseable_type: "PurchaseType", frequency: "Weekly", day: "Su", notes: "leave at gate", allergies: "peanuts", created_at: "2013-07-24 16:58:08", updated_at: "2013-07-24 16:58:08", size: nil, quantity: 1>, #<Purchase id: 43, user_id: 20, purchaseable_id: 8, purchaseable_type: "PurchaseType", frequency: "Weekly", day: "Su", notes: "leave at gate", allergies: "peanuts", created_at: "2013-07-24 16:58:08", updated_at: "2013-07-24 16:58:08", size: nil, quantity: 1>]>]
[:purchase, nil]
为什么不是每个集合项都作为局部变量被拾取purchase？
我把头发扯掉了，我确定这很愚蠢，我以前做过很多次，甚至将旧的工作代码与这个进行比较，我无法弄清楚问题是什么。要么是我在文档中没有看到的新 Rails 4 东西，要么我是个白痴。
谢谢！