创建餐厅菜单我应该使用has_many通过或habtm关联吗？

Question

I am attempting to create a Restaurant project and design the database for the menu. While creating the database schema, I seem to keep spinning my wheels on how to implement the correct associations among the following models MenuItem, Menu, and a Menu Section . Every time I go through the has_many :through , and has_and_belongs_to_many , I can see the benefits of both but then when I implement them I get confused. Additionally, I have the confusion of a self join to the mix which further throws me off.

I think that I am over engineering but some input into the database schema would be helpful. More specifically, which association should I use for the following scenario in your opinion?

So far I have three classes/tables Restaurant, Menu, and MenuItem and the scenario I have crafted:

class Restaurant
  has_many :menus  (#Desert, Drinks, Dinner, Lunch, etc.)
end

class Menu
  has_many :sections, class_name: "Menu", foreign_key: "sections_id"
  belongs_to :section, class_name: "Menu"

  has_many :menu_items, through: :sections

  belongs_to :restaurant
end

## Context for the Menu and Sections
If I had a drinks menu with the following sections, Non Alcoholic, 
Spirits, Wine, etc. These 'sections' are essentially menus with 
their own menu items. This is why I put a self join on the Menu 
class. Maybe Im mistaken.


 class MenuItem
   belongs_to :section, class_name: "Menu"
   belongs_to :menu
 end 

 ####
 The menu item for example of 'Yellow Tail Merlot' belongs to the 
 section "Wine" under the menu of "Drinks". This is precisely where
 I am getting thrown off. I get the feeling that I'm making this 
 too complicated but when I say it out loud to myself it makes 
 perfect sense. 

Ok so now here is version 2 with the habtm:

class Restaurant
  has_many :menus  (#Desert, Drinks, Dinner, Lunch, etc.)
end

class Menu
   has_and_belongs_to_many :menu_items
end


 class MenuItem
  has_and_belongs_to_many :menus
  has_and_belongs_to_many :sections, class_name: "Menu"
 end 

As you can see the above code in version 2 gets hairy. In fact, I don't even know if the sections part of has_and_belongs_to_many is possible. Anyways, this is my rationale taken from the Rails Associations docs.

A has_and_belongs_to_many association creates a direct many-to-many connection with another model, with no intervening model. For example, if your application includes menus and menu items, with each menu having many menu items and each menu item appearing in many menus, you could declare the models this way.

The quote is from the rails docs but I switched assemblies and parts with menus and menu items. Reading it that way makes complete sense. So now I ask, what do you guys think? Which would be better to use? Thank you.

Answer 1

I'd use belongs_to and instead of using a self join on the Menu table, create a new class/table called Section .

Updated would be:

class Restaurant
  has_many :menus
end

class Menu
  has_many :menu_items
  has_many :sections

  belongs_to :restaurant
end

class Section 
  belongs_to :menu
  has_many :menu_items
end


class MenuItem
  belongs_to :menu
  belongs_to :section
end 

The sections you describe are more categories, eg Wine is an alcoholic drink, Wine is the menu item and 'alcoholic drink' is the category. You could even go one step further and have Wine associated with two sections, 'alcoholic' and 'drink'.

Answer 2

should I use a has_many through or habtm association?

They both can be used to create similar many to many associations. The key difference is that has_and_belongs_to_many does not use a model for the join entities. While this sounds simple and appealing it does have some huge cons:

• There is no practical way to add access additional columns on the join table. For example you want to add an "position" column to sort the items - you´re out of luck with has_and_belongs_to_many .
• There is no way to directly query the join table.

So has_and_belongs_to_many is great for those zero complexity cases and not very good in real life. For everything else there is has_many through: .

class Restaurant
  has_many :menus
  has_many :menu_sections, through: :menus
  has_many :menu_items, through: :menu_sections
end

class Menu
  belongs_to :restaurant
  has_many :menu_sections
  has_many :menu_items, through: :menu_sections
end

class MenuSection
  belongs_to :menu
  has_one :restaurant, through: :menu
  has_many :menu_items
end

class MenuItem
  belongs_to :menu_section
  has_one :menu, through: :menu_section
  has_one :restaurant, through: :menu
end