RoR: ActiveRecord::RecordInvalid: Validation failed: Attendee must exist - ruby-on-rails

Question

I am trying to make a many-to-many association in an RoR program, but I can't get rid of the error I mentioned in the title, the command I am using in the Rails console is:
User.find(1).attended_events = [Event.find(1)]
I need to solve this problem and can't find anywhere, I appreciate any help.
My code:
Models
class User < ApplicationRecord
has_many :created_events,class_name:"Event"
has_many :hosts
has_many :attended_events, through: :hosts
end
class Host < ApplicationRecord
belongs_to :attended_event, class_name:"Event"
belongs_to :attendee, class_name:"User"
end
class Event < ApplicationRecord
belongs_to :creator, foreign_key: :user_id, class_name:'User'
has_many :hosts
has_many :attendees, through: :hosts
end
Migration Files
class CreateUsers < ActiveRecord::Migration[6.0]
def change
create_table :users do |t|
t.string :name
t.string :email
t.timestamps
end
end
end
class CreateHosts < ActiveRecord::Migration[6.0]
def change
create_table :hosts do |t|
t.references :attendee, null: false, foreign_key: true
t.references :attended_event, null: false, foreign_key: true
t.integer :user_id
t.integer :event_id
t.timestamps
end
end
end
class CreateEvents < ActiveRecord::Migration[6.0]
def change
create_table :events do |t|
t.string :date
t.text :description
t.references :user, null: false, foreign_key: true
t.timestamps
end
end
end

Answer 1

Read about the foreign_key option for has_many.
class Event < ApplicationRecord
belongs_to :creator, foreign_key: :user_id, class_name:'User'
has_many :hosts
has_many :attendees, through: :hosts
end
These model associations are wrong, the error is in the second line.
class Event < ApplicationRecord
belongs_to :creator, foreign_key: :user_id, class_name:'User'
has_many :hosts
has_many :attendees, through: :hosts
end
With these model associations, you need to specify the foreign_key for the has_many :hosts statement.
class Host < ApplicationRecord
belongs_to :attended_event, class_name:"Event"
belongs_to :attendee, class_name:"User"
end
Here are my suggestions:
User
class User < ApplicationRecord
has_many :created_events, foreign_key: 'user_id'
has_many :hosts, foreign_key: 'attendee_id'
has_many :attended_events, through: :hosts
end
Host
class Host < ApplicationRecord
belongs_to :attended_event, class_name: 'Event'
belongs_to :attendee, class_name: 'User'
end
Event
class Event < ApplicationRecord
belongs_to :creator, class_name: 'User'
has_many :hosts, foreign_key: 'attended_event_id'
has_many :attendees, through: :hosts
end
Your hosts migration
Better avoid passing the foreign_key here, it will look for an attendees table and a attended_events table in the database.
class CreateHosts < ActiveRecord::Migration[6.0]
def change
create_table :hosts do |t|
# t.references :attendee, null: false, foreign_key: true
t.references :attendee, null: false
# t.references :attended_event, null: false, foreign_key: true
t.references :attended_event, null: false
t.timestamps
end
end
end

Answer 2

Define source on through association
class User < ApplicationRecord
has_many :created_events, class_name:"Event"
has_many :hosts
has_many :attended_events, through: :hosts, source: :event
end
class Host < ApplicationRecord
belongs_to :event
belongs_to :user
end
class Event < ApplicationRecord
belongs_to :creator, foreign_key: :user_id, class_name:'User'
has_many :hosts
has_many :attendees, through: :hosts, source: :user
end
class CreateHosts < ActiveRecord::Migration[6.0]
def change
create_table :hosts do |t|
t.references :user, null: false, foreign_key: true
t.references :event, null: false, foreign_key: true
t.timestamps
end
end
end
Then you can do
User.find(1).attended_events << Event.find(1)