Rails 4: form_for associations

Question

New for rails and rubies. Fight with form_forand associations. I am trying to configure a rails application that allows a user to select from a list of clients. Customers are connected through relationships has_many :through. I have models working as expected, and I can add clients to users through the rails console. Now I want to move this feature to the web interface. Below is the code as I tried, but that just doesn't make sense to me. I'm not sure which controller action is the right action. Do I have to process the form POSTin client action? I really do not want to create a new client, I just want the user to select existing clients from the list and create an association.

My models:

class Client < ActiveRecord::Base
has_many :users, :through => :user_clients
has_many :user_clients, :dependent => :destroy
end

class User < ActiveRecord::Base
has_many :clients, :through => :user_clients
has_many :user_clients, :dependent => :destroy
end

class UserClient < ActiveRecord::Base
belongs_to :user
belongs_to :client
end

Routes as follows

resources :clients do
  resources :users
end

resources :users do
  resources :clients
end 

class ClientsController < ApplicationController
  before_action :set_client, only: [:show, :edit, :update, :destroy]

  def index
    if params[:user_id]
      @clients = User.find_by_id(params[:user_id]).clients
    else
      @clients = Client.all
    end
    @clients
  end

  def create
    if params[:user_id]
      user = User.find(params[:user_id])
      client = Client.find_by_id(params[:client_id])
      user.clients << client
      user.save
      redirect_to users_url
    else
      @client = Client.new(client_params)
      @client.save
      redirect_to clients_url
    end
  end
end

<h1>new.html.erb</h1>
<% if params[:user_id] %>
  <%= form_for([@user,@client]) do |f| %>
  <div class="field">
    <%= f.label :id %><br>
    <%= f.text_field :id %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
  <% end %>
<% else %>
  <%= render 'form' %>
<% end %>

Answer 1

-, : . railscasts . , , .

, !

. ​​ .

resources :clients do
  resources :users
end

resources :users do
  resources :clients
end 

. , users/:user_id/clients/new clients/new . , . Rails , - , , , . ( ) RESTful ( update ), - assign_client. :

resources :users do
  resources :clients
  member do
    put :assign_client
  end
end

, . , - , (- edit update). , .