How to access referenced table in a n:m relation in Ruby on Rails?

Question

I have got a Database like this:

    users
    -id

    user_cars
    -user_id
    -car_id

    cars
    -id
    -model
    -color

So a user can have multiple cars, and detailed information about the cars are in a big cars table. I also created the models with the relationships.

class User 
has_many :user_cars

class User_car
belongs_to :user
belongs_to :cars

class Car
has_many :user_cars

Now I want to access the information for all the cars for one user. My first approach would be to get at least one information (i.e. color) from the cars table.

I tried this one, just as an example for accessing the middle table:

@user_id = current_user.user_cars.find(1).user_id

works! But when I try to access the cars table I always get an error.

@color = current_user.user_cars.cars.find(1).color

undefined method `cars' for #<ActiveRecord::Relation:0xaf92e8c>

So I think Im doin something easy very wrong...

When I know how to get access to the third table, I have to do it in that fashion, that I only get results for the user and not just only the first entry, maybe you guys can help me with that aswell. Thanks!

Answer 1

The issue in your example by the way is that belongs_to should be singular. Also, your order was wrong.

@color = current_user.user_cars.find_by_car_id(1).car.color

You should rewrite this to use a has_many through association:

class User 
has_many :user_cars
has_many :cars, :through => :user_cars

class UserCar
belongs_to :user
belongs_to :car

You can then access the cars by doing:

current_user.cars

And the color by doing:

@color = current_user.cars.find_by_car_id(1).color

EDIT

After some debugging, it turns out that the Car model has a class property. Class is a reserved word in ruby. Be careful with naming your attributes!