Question

I have built a ruby on rails app that lets users track their workouts. User has_many workouts. In addition, a User can create a box (gym) if they are a gym owner. The purpose is to filter activity of users such that they can only see information related to their gym. Users can then specify if they are a member of that box through a Membership model. The Membership table collects @box.id and current_user.id in the membership.box_id and user.id columns respectively.

The user associates through the following form in the /views/boxes/show.html.erb view:

<% remote_form_for Membership.new do |f| %> 
  <%= f.hidden_field :box_id, :value => @box.id %>
  <%= f.hidden_field :user_id, :value => current_user.id %>
  <%= submit_tag "I am a member of this box" , :class => '' %>
<% end %>

I then display, in the box show page all the users who are members of that box.

<% @box.users.each do |user| %>
  <%= link_to (user.username), user %><br/>
<% end %>

I am trying to restrict the form to only users who are not already members of that box but I am not sure how to write the <% unless ... %> statement.

Here are the rest of the associations:

User

class User < ActiveRecord::Base
  has_many :boxes
  has_many :workouts, :dependent => :destroy
end

Workout

class Workout < ActiveRecord::Base
  belongs_to :user
  belongs_to :box
end

Box

class Box < ActiveRecord::Base
  belongs_to :user
  has_many :users, :through => :memberships
  has_many :workouts, :through => :users
  has_many :memberships
end

Membership

class Membership < ActiveRecord::Base
  belongs_to :user
  belongs_to :box
end

Answer 1

# Membership model
named_scope :for_box, lambda {|box| {:conditions => {:box_id => box.id}}}

# User model
has_many :memberships

def member_of_box?(box)
  !memberships.for_box(box).blank?
end

# View
<% unless current_user.member_of_box?(box) %>
   # Show the form
<% end %>

Disclaimer: The code is not tested. It might need minor alterations.