如何删除并返回ActiveRecord关系对象中的第一个元素？

Question

I want to remove and return the first element in an AR relation object. I used shift , but it does not remove the object.

With a normal array, shift works as expected:

a = [1, 2, 3]
a.shift # => 1
a # => [2, 3]

This does not work. The variable @attachment_versions retains the same size before and after using shift .

@attachment = Attachment.with_associations.find(params[:id])
@attachment_versions = @attachment.attachment_versions
@current_version = @attachment_versions.shift

# this raises `true`
raise @attachment_versions.include?(@current_version).to_s

def self.with_associations
  includes(attachment_versions: :owner, comments: [:author, :attachments])
end

I know that an AR relation object is more than just an Array, but I thought shift should work in the same way.

Answer 1

You can pretty easily turn it into an array first.

ie

@attachment_versions_array = @attachment_versions.to_a

@attachment_versions_array.shift
=> <Attachment_version......etc