Rails find with a block

Question

I have seen Rails find method taking a block as

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

Which is similar to Consumer.find(3).

Answer 1

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

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

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 }

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

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

Answer 2

The result may be similar, but the SQL query is not similar to Consumer.find(3)

It is fetching all the consumers and then filtering based on the block. I cant think of a use case where this might be useful

Here is a sample query in the console

 consumer = Consumer.find {|c|c.id == 2}
 # Consumer Load (0.3ms)  SELECT `consumers`.* FROM `consumers`
 # => #<Consumer id: 2, name: "xyz", ..>