Rails 找到一个块 [英] Rails find with a block

问题描述

我已经看到 Rails find 方法将一个块作为

I have seen Rails find method taking a block as

Consumer.find do |c|
  c.id == 3
end

类似于 Consumer.find(3).

Which is similar to Consumer.find(3).

在哪些用例中我们可以实际使用块进行 find ?

What are some of the use cases where we can actually use block for a find ?

推荐答案

它是 .to_a.find { ... } 的快捷方式.这是该方法的源代码::>

It's a shortcut for .to_a.find { ... }. Here's the method's source code:

def find(*args)
  if block_given?
    to_a.find(*args) { |*block_args| yield(*block_args) }
  else
    find_with_ids(*args)
  end
end

如果您传递一个块，它会调用 .to_a(加载所有记录)并调用 Enumerable#在数组上查找.

If you pass a block, it calls .to_a (loading all records) and invokes Enumerable#find on the array.

换句话说，它允许您在 ActiveRecord::Relation 上使用 Enumerable#find.如果您的条件无法在 SQL 中表达或评估，这会很有用，例如查询序列化属性:

In other words, it allows you to use Enumerable#find on a ActiveRecord::Relation. This can be useful if your condition can't be expressed or evaluated in SQL, e.g. querying serialized attributes:

Consumer.find { |c| c.preferences[:foo] == :bar }

为了避免混淆，我更喜欢更明确的版本:

To avoid confusion, I'd prefer the more explicit version, though:

Consumer.all.to_a.find { |c| c.preferences[:foo] == :bar }

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