Many-To-Many Association Query

Question

I have the following models:

class Restaurant < ApplicationRecord
  has_one_attached :image
  has_many :categories, through: :restaurant_category
end

class Category < ApplicationRecord
  has_many :restaurants, through: :restaurant_category
end

class RestaurantCategory < ApplicationRecord
  belongs_to :restaurant
  belongs_to :category
end

I would query in one shot all the categories associated to a restaurant. SOmething like this:

a = Restaurant.find(1)
a.restaurant_category 

But I have:

NoMethodError (undefined method `restaurant_category' for #<Restaurant:0x00007f5214ad2240>)

How can I solve it?

Answer 1

This:

class Restaurant < ApplicationRecord
  has_one_attached :image
  has_many :categories, through: :restaurant_category
end

... should look like this:

class Restaurant < ApplicationRecord
  has_one_attached :image
  has_many :restaurant_categories
  has_many :categories, through: :restaurant_categories
end

Similarly, this:

class Category < ApplicationRecord
  has_many :restaurants, through: :restaurant_category
end

... should look like this:

class Category < ApplicationRecord
  has_many :restaurant_categories
  has_many :restaurants, through: :restaurant_categories
end

Which you would use like:

restaurant_categories = Restaurant.find(1).categories

This is all explained in the has_many :through section of the Active Record Associations guide.