Faster element duplication

[mamhoff]

What is this pull request for?

This speeds up element duplication by picking all child elements from the source element's page version's element repository, the creating the new elements, without touching related database records or updating element positions.

The speedup here is considerable: In a tiny benchmark, we managed to reduce publishing time by more than half:

Main branch:

  0.820700   0.006808   0.827508 (  0.832897)

This branch:

  0.357914   0.004525   0.362439 (  0.364606)

The benchmark is the following file, feel free to add it to your project and try yourself:

require "rails_helper"
require "benchmark"

RSpec.describe Alchemy::Page::Publisher do
  describe "#publish!" do
    let!(:pages) do
      (0..10).map do
        page = create(:alchemy_page, autogenerate_elements: true)
        create(:alchemy_element, page_version: page.draft_version, parent_element: page.draft_version.elements.first)
        page
      end
    end

    it "is not so slow" do
      result = Benchmark.measure do
        pages.each { |page| described_class.new(page).publish!(public_on: Time.current) }
      end
      puts result
    end
  end
end

This is co-authored by @tvdeyen - I just cleaned up the commit history and added some specs.

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[tvdeyen]

Very nice. I think we can have accurate positions and the performance improvement.

[tvdeyen]

Very nice