为什么 Rails 3 中的 Model.all 与 Model.where('true') 不同
我有一个查询，效果很好：
ModelName.where('true')
我可以将其与其他 AR 调用（例如 where、order 等）链接起来。但是，当我使用时：
ModelName.all
我收到“相同”响应，但无法将 where 或 order 链接到它，因为它是数组而不是 AR 集合。 虽然我使用第一种方法没有任何实际问题，但它似乎有点丑陋/不必要。有没有更干净的方法可以做到这一点，可能是 .to_active_record_collection 或其他什么？
I have a query, which works fine:
ModelName.where('true')
I can chain this with other AR calls such as where, order etc. However when I use:
ModelName.all
I receive the "same" response but can't chain a where or order to it as it's an array rather than a AR collection.
Whereas I have no pragmatic problem using the first method it seems a bit ugly/unnecessary. Is there a cleaner way of doing this maybe a .to_active_record_collection or something?
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正如您所说，后者返回一个元素数组，而前者是一个 ActiveRecord::Relation。您可以使用 Ruby 方法对数组进行排序和过滤。例如，要按 id 排序，您可以调用
sort_by(&:id)。要过滤元素，您可以调用select或reject。对于ActiveRecord::Relation您可以将where或order链接到它，正如您所说。区别在于排序和处理的位置。对于Array来说，是由应用程序完成的；对于关系 - 通过数据库。当记录更多时，后者通常更快。它的内存效率也更高。
As you said, the latter returns an array of elements, while the former is an
ActiveRecord::Relation. You can order and filter array using Ruby methods. For example, to sort by id you can callsort_by(&:id). To filter elements you can callselectorreject. ForActiveRecord::Relationyou can chainwhereororderto it, as you said.The difference is where the sorting and processing goes. For Array, it is done by the application; for Relation - by the database. The latter is usually faster, when there is more records. It is also more memory efficient.
有一个简单的解决方案。而不是使用
使用：
There is an easy solution. Instead of using
Use:
正如您所说：
因此，只要不使用触发查询的
all、first或last，您就可以进行尽可能多的延迟加载。当您考虑缓存时，了解这些差异非常重要。
我仍然无法理解什么样的情况会导致您遇到类似的情况：
...除非您需要整堆资产用于一个目的，并从数据库中加载它，并需要其中的一个子集用于其他目的。对于这种情况，您需要使用 ruby 的数组过滤方法。
旁注：
永远不应该使用，它是一种反模式，因为您无法控制要检索的项目数量。并希望：
As you said:
So you can make as many lazy loading as long as you don't use
all,firstorlastwhich trigger the query.It's important to catch these differences when you consider caching.
Still I can't understand what kind of situation could lead you to something like:
... Unless you need the whole bunch of assets for one purpose and get it loaded from the database and need a subset of it to other purposes. For this kind of situation, you'd need to use ruby's Array filtering methods.
Sidenote:
should never be used, it's an anti-pattern since you don' control how many items you'll retrieve. And hopefully: