Ruby-on-rails Rails 3、Active Record 查询返回 ActiveRecord::Relation 对象，而不是对象
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Rails 3, Active Record query returns ActiveRecord::Relation object, instead of objects
提问by JP Silvashy
I feel like this is a simple problem I'm having due to my misunderstanding of the new ActiveRecord query interface, but take this example:
由于我对新的 ActiveRecord 查询接口的误解，我觉得这是一个简单的问题，但以这个例子为例：
>> Category.first.recipes
=> [ ... ] # array of recipes
However:
然而：
>> Category.where(:id => 1).recipes
=> NoMethodError: undefined method `recipes' for #<ActiveRecord::Relation:0x000001033dc9e0>
What's going on here? why does my wheremethod return an ActiveRecord::Relationobject? how can I retrieve the objects from the query here?
这里发生了什么？为什么我的where方法返回一个ActiveRecord::Relation对象？我如何从这里的查询中检索对象？
回答by Swanand
This is actually intentional.
这其实是故意的。
Category.where(:id => 1)
# Is Equivalent to Category.all(:conditions => {:id => 1}})
Category.where(:id => 1).first
# Is equivalent of Category.first(:conditions => {:id => 1}})
The objects are only retrieved when special methods like first, each etc are called. This is called lazy loading which is a great when you want to cache your views. Read more about why here.
仅在调用诸如 first、each 等特殊方法时才检索对象。这称为延迟加载，这在您想要缓存视图时非常有用。在此处阅读更多有关原因的 信息。
回答by Austin Lin
Category.where(:id => 1).recipes
Returns an array. If you simply do Category.where(:id => 1).first.recipesit should work.
返回一个数组。如果你只是这样做，Category.where(:id => 1).first.recipes它应该可以工作。
回答by cpuguy83
But if you are just doing a where against the id, use the find method
Category.find(1)will return a Category object.
So:Category.find(1).recipes
但是如果你只是针对 id 做一个 where，使用 find 方法
Category.find(1)会返回一个 Category 对象。
所以：Category.find(1).recipes
