Additional Foreign Key on a Join Table - mysql

Question

I have a join table joining a Client and a Setor (plural: setores) models. The relation is that a Client has_and_belongs_to_many Setores (there are three Setores, a Client can have from one to all three of them. Setores have lots of Clients).
My problem is:
In this join table I added a reference to the User model. Setores have many Users, but a relation between one client and one setor have only one user. But I don't know how to read and write this association on the clients_setores table.
My models are as follows:
class Client < ActiveRecord::Base
has_and_belongs_to_many :documents
has_and_belongs_to_many :setores
has_many :screenings
has_many :contacts
has_many :interactions, through: :contacts
validates :cnpj, uniqueness: true
class Setor < ActiveRecord::Base
self.table_name = 'setores'
has_many :documents
has_many :screenings
has_many :users
has_and_belongs_to_many :clients
attr_acessor :user_id
class User < ActiveRecord::Base
has_one :setores
has_many :clients
And the current join tables parameters that have been working appear like this on the end of Clients controller:
private
# Use callbacks to share common setup or constraints between actions.
def set_client
#client = Client.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def client_params
params.require(:client).permit(:cnpj, :pacote, :razsoc, :vencimento, user_ids:[], document_ids:[], setor_ids:[])
end
Note that "user_ids:[]" was my attempt to get it to work, which has failed so far.
In the views I use the current join tables like this (taken from /client/_form.html.erb):
<%= f.collection_check_boxes :setor_ids, Setor.where(pacote: true), :id, :setor do |b| %>
So with these checkboxes I can create an entry in the clients_setores table.
What I want to do is to be able to pick a User that belongs to a given setor_id from a drop down menu and store this relation in the join table. I did manage to make such menu appear with the following code, in the same _form.html.erb:
<%= f.collection_select :user_ids, User.where(:setor_id => 1), :id, :email %>
But when I submit the form, the values are not saved. I don't know if my problem is just that I didn't get the right way to record this association on my view or if my problem is further down in the controller (probably) and model (maybe).
Closest problem I found in SO was Rails 4 Accessing Join Table Attributes, but the association type is different (has_many/through) and there isn't a third relation involved, so I couldn't figure out how to make it work for me.

Answer 1

Example of many-to-many associations between three models, done with a single join table:
I start out by generating some models:
rails g model User; rails g model Setor; rails g model Client;
rails g model Joiner user_id:integer setor_id:integer client_id:integer
By the way, references is a way to add a foreign key that refers to an existing model. I.e. user:references will create a user_id column. It also adds an "index" to the foreign key, which improves the performance.
Then I add some associations to the classes
class Joiner
# columns: user_id, setor_id, client_id
belongs_to :user
belongs_to :setor
belongs_to :client
end
class User
has_many :joiners
has_many :setors, through: :joiners, source: :setor
has_many :clients, through: :joiners, source: :client
end
class Setor
has_many :joiners
has_many :users, through: :joiners, source: :user
has_many :clients, through: :joiners, source: :client
end
class Client
has_many :joiners
has_many :users, through: :joiners, source: :user
has_many :setors, through: :joiners, source: :setor
end
With this code written, you have many-to-many associations for the three models.
You can then write:
User.create; Setor.create;
Joiner.create(user_id: User.first.id, setor_id: Setor.first.id);
User.first.setors.length # => 1
This won't work for self-joins (i.e. a nested comment system), by the way, but that's not part of the question.

Answer 2

What I ended up doing to achieve the desired effect was to add three columns to the Client model:
userset1
userset2
userset3
This way a Client has up to three (since the field can be blank) relations with users, according to the Setores (departments) he has at his service.
This is the easiest solution in this case since I only have 3 Setores. It would not be for larger numbers.
If I had more than 3 Setores, making it impractical to keep adding columns in the Client table, I would cerate a new model just to store the relations, in this case, a table that would have, besides its unique ID, client_id, setor_id and user_id.