How do I create a join action between a group and a user?

Question

user.rb

  has_many :memberships, :dependent => :destroy
  has_many :groups, :through => :memberships

membership.rb

class Membership < ActiveRecord::Base
  attr_accessible :user_id, :group_id
  belongs_to :user
  belongs_to :group
  validates_uniqueness_of :user_id, :message => "You can only join one group!"

end

group.rb

has_many :memberships, :dependent => :destroy
has_many :users, :through => :memberships

groups_controller.rb

def join
    @group = Group.find(params[:id])
    @m = @group.memberships.build(:user_id => current_user.id)
    respond_to do |format|
      if @m.save
        format.html { redirect_to(@group, :notice => 'You have joined this group.') }
        format.xml  { head :ok }
      else
        format.html { redirect_to(@group, :notice => 'Join error.') }
        format.xml  { render :xml => @group.errors, :status => :unprocessable_entity }
      end
    end
  end

memberships_controller.rb

class MembershipsController < ApplicationController
before_filter :authenticate_user!
  def create
    @membership = current_user.memberships.build(:group_id => params[:group_id])
    if @membership.save
      flash[:notice] = "You have joined this group."
      redirect_to :back
    else
      flash[:error] = "Unable to join."
      redirect_to :back
    end
  end

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

Users have groups through a membership model which is a join table. My question. How do I create a join action for users to click on so that they can join a group?

From what I can see, you're already making the user join with two ways, from a user to a group or from a group to the `current_user`, what exactly is the problem? — Draiken, Aug 26 '11 at 17:35

score 2 · Answer 1 · answered Sep 14 '11 at 16:21

You've already completed step 1, which is adding the controller actions. Now you just need to add the appropriate route and wire it up in your views.

In your routes.rb:

resources :groups do
    get 'join', :on => :member
end

In your view file:

<%= link_to "Join this group", join_group_path(@group) %>

That's it!