How to write joins Rails ActiveRecord_Relation? - ruby-on-rails

Question

> u = User.first
> u.viewable_cars
OR
> Car.for(u)
would get me just the cars the user has permission to view but not the cars he owns! SQL in irb for both u.viewable_cars & Car.for(u), which is the same, cars with id 1 to 50 which belongs to user don't get called at all:
SELECT "cars".* FROM "cars" INNER JOIN "permissions" ON "permissions"."thing_id" = "cars"."id" AND "permissions"."thing_type" = $1 WHERE ((cars.user_id = 1) OR (permissions.action = 'view' AND permissions.user_id = 1)) ORDER BY created_at DESC [["thing_type", "Car"]]
=> #<ActiveRecord::Relation [#<Car id: 52, content: "sport edition", name: "BMW", user_id: 2, created_at: "2014-11-01 04:58:19", updated_at: "2014-11-01 04:58:19">, #<Car id: 51, content: "super sport car", name: "BMW M6", user_id: 3, created_at: "2014-11-01 04:44:31", updated_at: "2014-11-01 04:44:31">]>
class Car < ActiveRecord::Base
belongs_to :user
has_many :permissions, as: :thing
default_scope -> { order('created_at DESC') }
validates :user_id, presence: true
validates :name, presence: true, length: { maximum: 50 }, uniqueness: true
validates :content, length: { maximum: 300 }, allow_blank: true
scope :viewable_by, ->(user) do
joins(:permissions).where(permissions: { action: "view",
user_id: user.id })
end
scope :for, ->(user) do
joins(:permissions).
where("(cars.user_id = :user_id) OR (permissions.action = 'view' AND permissions.user_id = :user_id)", user_id: user.id)
end
end
class User < ActiveRecord::Base
...
has_many :cars, dependent: :destroy
has_many :permissions
has_many :viewable_cars, ->(user) { joins(:permissions).
where("(cars.user_id = :user_id) OR (permissions.action = 'view' AND permissions.user_id = :user_id)", user_id: user.id) },
class_name: "Car"
def viewable_cars
Car.for(self)
end
end
class Permission < ActiveRecord::Base
belongs_to :user
belongs_to :thing, polymorphic: true
end
Rails.application.routes.draw do
resources :users do
resources :cars
end
end

Answer 1

Your scope for in car.rb should be this:
scope :for, ->(user) do
joins("LEFT OUTER JOIN permissions ON permissions.thing_id = cars.id AND permissions.thing_type = 'Car'").where("(cars.user_id = :user_id) OR (permissions.action = 'view' AND permissions.user_id = :user_id)", user_id: user.id)
end
Now you can do: Car.for(current_user).find(params[:id]). However, this looks like an antipattern to me. So you can create another association in user.rb like this:
Rails 4:
has_many :viewable_cars, ->(user) {
joins("LEFT OUTER JOIN permissions ON permissions.thing_id = cars.id AND permissions.thing_type = 'Car'").
where("(cars.user_id = :user_id) OR (permissions.action = 'view' AND permissions.user_id = :user_id)", user_id: user.id) },
class_name: 'Car'
Rails 3(couldn't find a better way of doing it, e.g.: associations):
def viewable_cars
Car.for(self)
end
So that you can fetch all cars for user:
current_user.viewable_cars
In controller:
#car = current_user.viewable_cars.find(params[:id])