HMT或HABTM用于订单和物品

Question

Fairly new to rails and trying to understand which relationships to use before going forward.

I have two models: orders and items . This is a many to many relationship, but I'm unsure of which relationship to use.

Orders might have delivery time, quantity of items, etc.

Lastly, what would you call the model joining orders and items if using HMT?

Answer 1

If you need to know anything else about the relationship of the item on a particular order, you need HMT.

If your items change price in the future, do you want to know how much they were sold for on orders in the past?

In this type of requirement, I've always had many "LineItem" records for an order, and the line_item instances belong_to to the item and order, and record the pricing and/or quantity for that order.

HMT vs HABTM? There are so few times that all you need is a many-to-many, that I'd almost always go with HMT for the extra ability to add more information to the association.

Answer 2

This seems like a classic case of HABTM, and the example given in the Rails Guides is perfect. The choice comes down to whether you need any other data or logic on the join model itself. If so, then use the HMT, where you will create a third active_record model to serve as the join table. You can name that anything you want. But it seems like HABTM will work for you, and all you need to setup is the join table with the default name ( items_orders ) in your migration, and rails will take care of everything else for you.

class Order < ActiveRecord::Base
  has_and_belongs_to_many :items
end

class Item < ActiveRecord::Base
  has_and_belongs_to_many :orders
end