How to Use joins and includes for Grandchild and Great-Grandchild Models in Rails ActiveRecord (Deeply Nested Includes)

Relationship Diagram

AAAs
┣BBBs
┃　┣CCCs
┃　┃　┗FFFs
┃　┗DDDs
┗GGGs

How to do it

AAAs.includes(:BBBs) # Child
AAAs.includes(BBBs: :CCCs) # Grandchild
AAAs.includes(:GGGs, BBBs: [:CCCs, :DDDs]) # Children and grandchildren
AAAs.joins(BBBs: [{CCCs: :FFFs}, :DDDs]) # With great-grandchildren

References

• Ruby on Rails - Avoid N+1 Query with Include and Join | Leon's Blogging
  • https://mgleon08.github.io/blog/2016/01/10/ruby-on-rails-include-join-avoid-n-1-query/
• Rails ActiveRecord/SQL Tips | Qiita
  • https://qiita.com/tomomomo1217/items/1ccd21bfb97730763255#孫モデルをincludes
• Joins/Includes and where search across multiple tables in Rails | EasyRamble
  • https://easyramble.com/rails-multi-tables-joins-includes-where.html
• Including across multiple tables in Rails | Nomu-dari Netari
  • http://nomnel.net/blog/rails-multi-table-includes/