Models association: where to put the foreign_key

Question

I`m working on a project that controls the equipment lendings to users.

It displays the lending view that renders a form where user can choose the equipment that he/she wants through a select box.If the equipment is not available in select box, user have to register the equipment then it will appear in that select box in lending view's form.

Model Association:

Lending has_many Equipment

Equipment belongs_to Lending

The doubt is: If Equipment belongs_to Lending then I must put the lending_id in Equipment.

But if user access the new equipment view and try to register a new equipment it will miss the lending_id.

How can I solve this?

Answer 1

My guess is what you really want is for lending to be a many-to-many mapping of users to equipments.

class User < ActiveRecord::Base
    has_many :lendings
    has_many :equipments, :through => :lendings

    # etc
end

class Equipment < ActiveRecord::Base
    has_many :lendings
    has_many :users, :through => :lendings

    # etc
end

class Lending < ActiveRecord::Base
    belongs_to :user
    belongs_to :equipment

    # etc
end

You can write methods to give the "current" user for an equipment via the latest active lending, and vice-versa, plus you have a convenient history of all lendings of an item of equipment.