ruby on rails: list records that does not match a given set of ids

Question

So, I have three models:

class Restaurant < ActiveRecord::Base
  has_many :reviews
  has_many :users, through: :reviews
end

class Review < ActiveRecord::Base
  belongs_to :restaurant
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :reviews
  has_many :restaurants, through: :reviews
end

Now, if I want to list all restaurants reviewed by @user I just need:

Restaurant.joins(:reviews).where("reviews.user_id": @user.id)

Fine. But what if I want to list all restaurants not reviewed by @user? I tried this:

Restaurant.joins(:reviews).where.not(“reviews.user_id": @user.id)

Unfortunately this doesn’t work, as it will also return those restaurants reviewed by @user that have been reviewed by other users!

I came up with this horrible and expensive hack:

Restaurant.joins(:reviews).reject {|x| x.users.where(id: @user.id).present? }

I’m sure there MUST be a better way. HELP!

Answer 1

It's pretty easy.

You have to map the ids of all restaurants reviewed by @user

reviewed_restaurants = Restaurant.joins(:reviews).where("reviews.user_id": @user.id).map(&:id)

Then fire another query to fetch restaurants other than those selected before

@unreviewed_restaurants = Restaurant.where("id not in (?)", reviewed_restaurants)

Hope it works for you.