Rails 4：查找所有记录 [英] Rails 4: find all records

问题描述

现在在Rails 4中已弃用ActiveRecord :: Relation＃all了，您应该如何迭代所有记录？

Now that ActiveRecord::Relation#all is deprecated in Rails 4, how are you supposed to iterate all records?

以前是这样的：

Foo.all.each do |foo|
  # whatever
end

我现在可以这样近似，但是感觉很脏：

I can approximate it now like so, but it feels dirty:

Foo.where(true).each do |foo|
  # whatever
end

有更好的方法吗？

推荐答案

根据活动记录查询界面上的路轨指南，遍历所有记录的正确方法是使用 find_each 。

According to the Rails Guide on Active Record Query Interface, the correct way to iterate through all records is by using find_each.

使用 Foo.all.each 会将 entire 表加载到内存中，实例化所有行；然后遍历实例。 find_each 分批执行此操作，这在内存使用方面更为有效。

Using Foo.all.each will load the entire table into memory, instantiating all the rows; then iterate through the instances. find_each does this in batches, which is more efficient in terms of memory usage.

来自指南：

find_each 方法检索一批记录，然后生成每条记录作为模型分别记录到块中。在下面的示例中， find_each 将检索1000条记录（ find_each 和的当前默认设置） find_in_batches ），然后将每个记录作为模型分别生成到块中。重复此过程，直到处理完所有记录为止：

The find_each method retrieves a batch of records and then yields each record to the block individually as a model. In the following example, find_each will retrieve 1000 records (the current default for both find_each and find_in_batches) and then yield each record individually to the block as a model. This process is repeated until all of the records have been processed:

User.find_each do |user|
  NewsLetter.weekly_deliver(user)
end

参考文献：

• 活动记录查询界面


• ActiveRecord :: Batches

• Active Record Query Interface
• ActiveRecord::Batches

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