Question

I’m getting rather confused about foreign keys in the join table. I’m trying to build a join table that links my user and guideline models to form a FavoriteGuideline table (i.e. user can pick a favorite guideline).

My error is:

‘Expected FavoriteGuideline to have a belongs_to association called
favorite (FavoriteGuideline does not have a favorite_id foreign key)’

My favorite_guideline.rb is

class FavoriteGuideline < ActiveRecord::Base
belongs_to :user
belongs_to :guideline
belongs_to :favorite, class_name: 'User', foreign_key: 'favorite_id'

attr_accessible :user, :favorite, :guideline
end

and my favorite_guideline_test.rb is

require 'test_helper'

class FavoriteGuidelineTest < ActiveSupport::TestCase
  should belong_to(:user)
  should belong_to(:favorite)

  test "that creating a favorite works without raising an exception" do

    assert_nothing_raised do 
    FavoriteGuideline.create user: users(:eve), guideline: guidelines(:three)

  end
end
end

And my database migration is

class CreateFavoriteGuidelines < ActiveRecord::Migration
def change
create_table :favorite_guidelines do |t|
        t.integer :user_id
        t.integer :favorite_id
        t.integer :guideline_id
  t.timestamps
end

add_index :favorite_guidelines, [:user_id]
add_index :favorite_guidelines, [:favorite_id]
add_index :favorite_guidelines, [:guideline_id]
end
end

Answer 1

If I understand correctly, FavoriteGuideline is meant to be the association table. Favorite is just an alias for FavoriteGuideline.

So your model should be:

class FavoriteGuideline < ActiveRecord::Base
set_primary_key 'favorite_id'
belongs_to :user
belongs_to :guideline

attr_accessible :user, :favorite, :guideline
end

And your test should have the line

should belong_to(:guideline)

instead of

should belong_to(:favorite)

And your migration should probably have favorite_id as the primary key:

def change
create_table :favorite_guidelines, :primary_key => :favorite_id do |t|
        t.integer :user_id
        t.integer :guideline_id
  t.timestamps
end

Then you will also need to finish defining the association with has_many in user.rb and guideline.rb