includes vs joins

includes: for nested associations

Model associations:

• a_model has many b_models
• b_model has many c_models
• b_model has many d_models
• d_model has one e_model

AModel.includes(b_models: [{ d_models: :e_model }, :c_models]).find(1)

# Code source: RailsGuides
# [13.1.2 Nested Associations Hash]
# http://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations
Category.includes(articles: [{ comments: :guest }, :tags]).find(1)

Model associations:

NOTE: menu_category was designed not to share with other menus, so the association was defined as above.

• menu has many menu_categories
• menu_category has many menu_items

@menu = Menu.includes(menu_categories: :menu_items).find_by_name(menu)

Reference

• Includes vs Joins in Rails: When and where?
• 3 ways to do eager loading (preloading) in Rails 3 & 4
• 13.1 Eager Loading Multiple Associations