How to access data out of a join table in Rails 3

Question

I have a has_and_belongs_to_many association between a user and a task.

I wanted a user to join a task and created an action in the user controller as follows:

  def joinTask
    @user = current_user
    @task = Task.find(params[:id])
    @users_tasks =  @task
    @task.save

    respond_to do |format|
      if @task.update_attributes(params[:task])
        format.html { redirect_to [@task.column.board.project, @task.column.board], notice: 'You joined the task successfully' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @task.errors, status: :unprocessable_entity }
      end
    end
  end

To see if that is properly working I wanted to list all users that belong to a specific task. For that I added an action to the user controller where I am trying to get all users that belong to a task:

def showTeam
    @users = Task.find(params[:id]).users

    respond_to do |format|
      format.html # showTeam.html.erb
      format.json { render json: @users}
    end
end

But I always get the error

undefined method `name' for nil:NilClass

when it tries to render the html page to get the users names...

Am I on the wrong track?

Models:

class Task < ActiveRecord::Base
  attr_accessible :description, :title, :weight, :story_id, :column_id, :board_id

  belongs_to :story, :foreign_key => "story_id"
  belongs_to :column, :foreign_key => "column_id"
  has_and_belongs_to_many :users

end

class User < ActiveRecord::Base

 attr_accessible :name, :login, :email, :password, :password_confirmation, :status
 has_and_belongs_to_many :projects
 has_and_belongs_to_many :tasks
end

I call the actions:

<%= link_to 'Join task', joinTask_path(task), :class => 'btn' %>
<%= link_to 'Show Team', showTeam_path(task), :class => 'btn' %>

The rootes are defined as follows:

match "joinTask_user/:id" => "users#joinTask", :as => :joinTask
match "showTeam_task/:id" => "tasks#showTeam", :as => :showTeam

And in the end the showTeam.html.erb is rendered and there I want to access the users name:

<p>
  <b>Name:</b>
  <%= @user.name %>
</p>

Can you also post your `User` and `Task` model files as well, please. — paracycle, Jul 10 '12 at 12:43

score 0 · Accepted Answer · answered Jul 10 '12 at 14:47

It seems like you're never creating a relation between your users and tasks.

@user = current_user
@task = Task.find(params[:id])
@users_tasks =  @task
@task.save

I think what you meant is

@task = Task.find(params[:id])
@task.users << current_user
@task.save

You shouldn't have to use the update_attributes. ]

Also, in your show view, you're loading @users, but you're calling @user.name.

If you want to show all the user names, it should be more along the lines of

<% @users.each do |user| %>
  <p>
    <b>Name:</b>
    <%= user.name %>
  </p>
<% end %>

You can verify if you have a relation in rails console by finding your task and calling task.users on it.

In any case, if you're just starting this project, I suggest reading on nested resources for your tasks as this is the typical use case for them.

How to access data out of a join table in Rails 3

1 Answers1