Issues with creating a "many-to-many" relation - ruby-on-rails

Question

I'm trying to do a simple task : I created a "magazine" scaffold, but I want it to have a specific relation : a user can have participate for the creation / redaction of a magazine, and it can take several users to create a magazine.
I checked the APIDock and did the following:
Specified the relation between the magazines and the users
model/magazine.rb
class Magazine < ApplicationRecord
mount_uploader :thumbnail, ThumbnailUploader
has_and_belongs_to_many :users
end
model/user.rb
class User < ApplicationRecord
has_and_belongs_to_many :magazines
# More code...
end
Created a migration to add a table to link both the models
class ManyToMany < ActiveRecord::Migration[5.0]
def change
create_table :magaziness_users, :id => false do |t|
t.integer :user_id
t.integer :magazine_id
end
add_index :magazines_users, [:magazine_id, :user_id]
end
end
Then I ran the migration
Added the list of all users ever recorded to the database to create a dropdown
<div class="field">
<%= f.label :users %>
<%= f.select :users, User.all_except(current_user).collect {|u| [u.username, u]}, {prompt: 'Add a creator?'}, { :multiple => true, :size => 3 } %>
</div>
But, when I'm saving a new magazine, the user doesn't get saved, and the "magazines_user remains empty.
edit 1
This is an auto-generated controller, since I use the scaffold command to create it. I didn't touch anything excepted the set_magazine function, where I added the Friendly_Id
class MagazinesController < ApplicationController
before_action :set_magazine, only: [:show, :edit, :update, :destroy]
def index
#magazines = magazine.all
end
def show
end
def new
#magazine = magazine.new
end
def edit
end
def create
#magazine = magazine.new(magazine_params)
if #magazine.save
redirect_to #magazine, notice: 'magazine was successfully created.'
else
render :new
end
end
def update
if #magazine.update(magazine_params)
redirect_to #magazine, notice: 'magazine was successfully updated.'
else
render :edit
end
end
def destroy
#magazine.destroy
redirect_to magazines_url, notice: 'magazine was successfully destroyed.'
end
private
def set_magazine
#magazine = magazine.friendly.find(params[:id])
end
def magazine_params
params.require(:magazine).permit(:titre, :description, :apercu, :users)
end
end
Did I forget any step?

Answer 1

so here is the answer with my code working:
I did two scaffolds:
rails generate scaffold user username:string email:uniq password:digest
rails generate scaffold magazine title:string description:text preview:string
Then added this to magazine migration:
create_table :magazines_users, id: false do |t|
t.belongs_to :magazine, index: true
t.belongs_to :user, index: true
end
In my form, I added:
<div class="field">
<%= f.label :users %>
<%= f.select :user_ids, User.all.collect { |u| [u.username, u.id] }, {include_blank: true}, {multiple: true} %>
</div>
And in my magazines controller I only modified magazine_params:
def magazine_params
params.require(:magazine).permit(:title, :description, :preview, :user_ids => [])
end
To see that it works, I added this in magazin show view:
<p>
<strong>Users:</strong>
<%= #magazine.users.map(&:username).join(" - ") %>
</p>
Of course I added "has_and_belongs_to_many" as you did in User and Magazine models.
And that's it :)
Tested with Rails 5 and it works just fine. :)
Also I strongly advice you to take a look at the simple_form gem. It has some great methods to handle associations (like has_and_belongs_to_many) easily, like this : <%= f.association :users, collection: User.all_except(current_user).order(:username) %>