# == Schema Information
#
# Table name: emergencies
#
#  id              :integer          not null, primary key
#  activated_by_id :integer
#
# Indexes
#
#  index_emergencies_on_activated_by_id  (activated_by_id)

class Emergency < ActiveRecord::Base
  belongs_to :activated_by, primary_key: 'id', foreign_key: 'activated_by_id', class_name: 'Company'
end

# == Schema Information
#
# Table name: companies
#
#  id              :integer          not null, primary key
#  name            :string

class Company < ActiveRecord::Base
  has_many :emergencies, primary_key: 'id', foreign_key: 'activated_by_id', class_name: 'Emergency'
  validates :name, presence: true, uniqueness: true
end

Emergency.first.activated_by.name
Company.first.emergencies

Area has_many loops Loop belongs_to Area

# loop/index.html.erb
<td><%= loop.area.name %></td>

# area/_form.heml.erb
  <div class="field">
    <%= f.label :area_id %><br>
    <%= f.select :area_id, Area.all.map { |area| [area.name, area.id] }, include_blank: true %>
  </div>

Source: http://apidock.com/rails/ActiveRecord/Associations/ClassMethods/has_and_belongs_to_many

# == Schema Information
#
# Table name: loops
#
#  id         :integer          not null, primary key
#  name       :string
#  coord_x    :decimal(, )
#  coord_y    :decimal(, )
#  created_at :datetime
#  updated_at :datetime
#  area_id    :integer

class Loop < ActiveRecord::Base
  has_and_belongs_to_many :gates
  belongs_to :area
  has_many :emergencies
  validates :name, presence: true, uniqueness: true
end

# == Schema Information
#
# Table name: gates
#
#  id         :integer          not null, primary key
#  name       :string
#  coord_x    :decimal(, )
#  coord_y    :decimal(, )
#  created_at :datetime
#  updated_at :datetime
#
class Gate < ActiveRecord::Base
  has_and_belongs_to_many :loops
  validates :name, presence: true, uniqueness: true
end

l = Loop.first
l.gates << Gate.first

# loops/_add_gates.html.erb
<h3>Add gates</h3>
<%= form_tag loops_path do %>
<div class="field">
  <%= label_tag :gate %>
  <%= collection_select :gate, :id, Gate.all, :id, :name, include_blank: true %>
</div>
<div class="actions">
  <%= submit_tag %>
</div>
<% end %>

class Project < ActiveRecord::Base
    validates :name, presence: true, uniqueness: true
    has_many :activities
    has_many :tasks, -> { uniq }, through: :activities
    has_many :users, -> { uniq }, through: :activities
    scope :how_many_new_activity, -> { limit(5) }
end