#163 Self-Referential Association

May 25, 2009 | 14 minutes | Active Record, Controllers

Creating a social networking site often requires a self-referential association on the User model to define friends/followers. In this episode I show how to do exactly that.

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          bash
        
script/generate nifty_scaffold friendship user_id:integer friend_id:integer create destroy
rake db:migrate

          models/user.rb
        
has_many :friendships
has_many :friends, :through => :friendships
has_many :inverse_friendships, :class_name => "Friendship", :foreign_key => "friend_id"
has_many :inverse_friends, :through => :inverse_friendships, :source => :user

          models/friendship.rb
        
belongs_to :user
belongs_to :friend, :class_name => "User"

          friendships_controller.rb
        
def create
  @friendship = current_user.friendships.build(:friend_id => params[:friend_id])
  if @friendship.save
    flash[:notice] = "Added friend."
    redirect_to root_url
  else
    flash[:error] = "Unable to add friend."
    redirect_to root_url
  end
end

def destroy
  @friendship = current_user.friendships.find(params[:id])
  @friendship.destroy
  flash[:notice] = "Removed friendship."
  redirect_to current_user
end

          users/index.html.erb
        
<%= link_to "Add Friend", friendships_path(:friend_id => user), :method => :post %>

          users/show.html.erb
        
<h2>Friends</h2>
<ul>
  <% for friendship in @user.friendships %>
    <li>
      <%=h friendship.friend.username %>
      (<%= link_to "remove", friendship, :method => :delete %>)
    </li>
  <% end %>
</ul>

<p><%= link_to "Find Friends", users_path %></p>

<h2>Friended by Users</h2>
<ul>
  <% for user in @user.inverse_friends %>
    <li><%=h user.username %></li>
  <% end %>
</ul>