具有相同模型的Ruby on Rails 4的多态关联

Question

So I have an app in which users can create cars. They can also like cars and I want to create an association between both. Cars that they created belong to them and Cars that they have liked belong to them through the context of liking them. To do this I have set up my associations as follows:

User Association:

class User < ActiveRecord::Base
  has_many :cars
  has_many :cars, -> {distinct}, through: :likes
end

Car Association:

class Car < ActiveRecord::Base
  belongs_to :users
  has_many :likes
  has_many :users, -> { distinct }, through: :likes
 end

Like Association:

class Like < ActiveRecord::Base
 belongs_to :user
 belongs_to :car
end

The problem is that before I had my user has_many cars through like relationship declared. I used to be able to call @user.cars and it would present the user's cars. Now it returns the collection of the cars the user has liked. I need methods for each collection.

When I try: User.likes.cars

I get a

No Method error

and the console log looks through the likes records and still doesn't return the cars even though my likes records have a car_id field.

I have looked at a bunch of questions but have trouble understanding them. I've also tried to define methods in the model and nothing is seeming to work. Any help is appreciated.

How would I be able to change my associations so I can have a for query both User.cars (for cars the user has created) and User.likes.cars (for cars the user has liked)?

Answer 1

So the below answer from Oleg didn't work exactly but led me in the right direction. Thank you! I started by following the above example and doing:

    class User < ActiveRecord::Base
       has_many :cars
       has_many :car_likes, -> {distinct}, class_name: 'Car', through: :likes
     end

     class Car < ActiveRecord::Base
       belongs_to :users
       has_many :likes
       has_many :user_likes, -> { distinct }, class_name: 'User', through: :likes
      end

This returned the following error in console:

ActiveRecord::HasManyThroughSourceAssociationNotFoundError: Could not find the source association(s) "car_likes" or :car_like in model Like. Try 'has_many :car_likes, :through => :likes, :source => '. Is it one of user or car?

So I changed it to:

class User < ActiveRecord::Base
  has_many :cars
  has_many :car_likes, -> {distinct}, through: :likes, source: :cars
end
Car Association:

class Car < ActiveRecord::Base
  belongs_to :users
  has_many :likes
  has_many :user_likes, -> { distinct }, through: :likes, source: :users
 end

It nows works for both models! Thanks and hopefully this is helpful to someone else with the same problem.

Answer 2

has_many :cars, -> {distinct}, through: :likes overrides has_many :cars because it redefines User.cars . Try the following:

class User < ActiveRecord::Base
  has_many :cars
  has_many :car_likes, -> {distinct}, class_name: 'Car', through: :likes
end
Car Association:

class Car < ActiveRecord::Base
  belongs_to :users
  has_many :likes
  has_many :user_likes, -> { distinct }, class_name: 'User', through: :likes
 end

#To get them, instead of user.likes.cars
@user.car_likes
@car.user_likes

Please let me know if the problem persists. There might be another error.

Answer 3

I don't see where you are defining any model as polymorphic.

In the past I have done something like this.. actually I did this for tags/taggings and made "like" a tag a user applied to another instance. This is an ad-hoc modification and I may have missed something but it's a pretty common use case for polymorphic associations.

class Like < ActiveRecord::Base
  belongs_to :likeable, polymorphic: true
  ...
end

class Liking < ActiveRecord::Base
  belongs_to :like
  belongs_to :likeable, :polymorphic => true
end

class User < ActiveRecord::Base
  has_many :likings, :as => :likeable
  has_many :likes,  -> { order(created_at: :desc) }, :through => :taggings
end