Struggling to add has_many through relationship

Question

I am trying to make a has_many through relationship like this:

#user.rb
class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  has_many :availabilities
  has_many :timeslots, :through => availabilities
end

#availability.rb
class Availability < ApplicationRecord
    belongs_to :timeslot
    belongs_to :user
end

#timeslot.rb
class Timeslot < ApplicationRecord
    has_many :availabilities
    has_many :timeslots, :through => availabilities
end

I created the two models and than ran rake db:migrate without adding the code in the models (to create the tables). I made a migration file:

class AddFieldsToTables < ActiveRecord::Migration[5.0]
  def change
    add_column :users, :availability_id, :integer
    add_column :timeslots, :availability_id, :integer
    add_column :availabilities, :user_id, :integer
    add_column :availabilities, :timeslot_id, :integer
  end
end

and ran rake db:migrate Than I added the code above to all the files. And then if I try to generate anything it gives me NameError: undefined local variable or method availabilities for User (call 'User.connection' to establish a connection):Class

I am new to Ruby on Rails.

Answer 1

I see a tiny problem in your code:

#timeslot.rb
class Timeslot < ApplicationRecord
    has_many :availabilities
    has_many :timeslots, :through => availabilities
end

it should be:

#timeslot.rb
class Timeslot < ApplicationRecord
    has_many :availabilities
    has_many :users, :through => availabilities
end

I'm not sure if it can solve your problem but your code (exclude the above mistake) sounds fine for me.

Answer 2

One issue I see is that in your timeslot.rb you have has_many :timeslots, :through => availabilities . I'm guessing you want has_many :users, :through => :availabilites .

Another is in user.rb , you have has_many :timeslots, :through => availabilities but you need the symbol :availabilites . This is what is causing the error you posted, I believe. It should look like this (all I've changed is the second-to-last line):

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  has_many :availabilities
  has_many :timeslots, :through => :availabilities
end

Answer 3

In order to setup has_many through relationship between two tables users and timeslots , you need to setup join table availabilities with columns user_id and timeslot_id .

Setup your rails models like below:

# models/user.rb
class User < ApplicationRecord
  has_many :availabilities
  has_many :timeslots, :through => :availabilities
end

# models/availability.rb
# projects table should have these columns - user_id:integer, timeslot_id:integer
class Availability < ApplicationRecord
  belongs_to :timeslot
  belongs_to :user
end    

# models/timeslot.rb
class Timeslot < ApplicationRecord
  has_many :availabilities
  has_many :users, :through => :availabilities
end

You need a migration to create availabilities table which acts as a join table for your has_many through relationship between Timeslot Object and User Object. Migration file looks something like this:

class CreateAvailabilities < ActiveRecord::Migration[5.0]
  def change
    create_table :availabilities do |t|
      t.integer :user_id
      t.integer :timeslot_id
    end
  end
end

Access

User.last.timeslots gives 0, 1 or many timeslots associated with User.last

Timeslot.last.users gives 0, 1 or many users associated with Timeslot.last