ruby on rails has_many通过关系

Question

Hi i'm having a little trouble with a has_many through relationship for my app and was hoping to find some help. So i've got Users & Lectures. Lectures are created by one user but then other users can then "join" the Lectures that have been created. Users have their own profile feed of the Lectures they have created & also have a feed of Lectures friends have created. This question however is not about creating a lecture but rather "Joining" a lecture that has been created already. I've created a "lecturerelationships" model & controller to handle this relationship between Lectures & the Users who have Joined (which i call "actives"). Users also then MUST "Exit" the Lecture (either by clicking "Exit" or navigating to one of the header navigation links). I'm grateful if anyone can work through some of this with me...

I've got: Users.rb model Lectures.rb model Users_controller Lectures_controller

then the following model

lecturerelationship.rb

class lecturerelationship < ActiveRecord::Base
  attr_accessible :active_id, :joinedlecture_id

  belongs_to :active, :class_name => "User"
  belongs_to :joinedlecture, :class_name => "Lecture"

  validates :active_id, :presence => true
  validates :joinedlecture_id, :presence => true

end

lecturerelationships_controller.rb

class LecturerelationshipsController < ApplicationController
  before_filter :signed_in_user

  def create
   @lecture = Lecture.find(params[:lecturerelationship][:joinedlecture_id])
   current_user.join!(@lecture)
   redirect_to @lecture
  end

 def destroy
  @lecture = Lecturerelationship.find(params[:id]).joinedlecture
  current_user.exit!(@user)
  redirect_to @user
 end

end

Lectures that have been created (by friends) show up on a users feed in the following file

_activity_item.html.erb

<li id="<%= activity_item.id %>">
  <%= link_to gravatar_for(activity_item.user, :size => 200), activity_item.user %><br   clear="all">
  <%= render :partial => 'shared/join', :locals => {:activity_item => activity_item} %>
  <span class="title"><%= link_to activity_item.title, lecture_url(activity_item)  %></span><br clear="all">
  <span class="user">
   Joined by <%= link_to activity_item.user.name, activity_item.user %>
  </span><br clear="all">
  <span class="timestamp">
   <%= time_ago_in_words(activity_item.created_at) %> ago.
  </span>
  <% if current_user?(activity_item.user) %>
    <%= link_to "delete", activity_item, :method => :delete,
                                     :confirm => "Are you sure?",
                                     :title => activity_item.content %>
  <% end %>
</li>

Then you see I link to the the 'shared/join' partial above which can be seen in the file below

_join.html.erb

<%= form_for(current_user.lecturerelationships.build(:joinedlecture_id =>  activity_item.id)) do |f| %>
  <div>
   <%= f.hidden_field :joinedlecture_id %>
  </div>
  <%= f.submit "Join", :class => "btn btn-large btn-info" %>
<% end %>

Some more files that might be needed:

config/routes.rb

SampleApp::Application.routes.draw do
  resources :users do
    member do
    get :following, :followers, :joined_lectures
  end
end

resources :sessions, :only => [:new, :create, :destroy]
resources :lectures, :only  => [:create, :destroy, :show]
resources :relationships, :only => [:create, :destroy] #for users following each other
resources :lecturerelationships, :only => [:create, :destroy] #users joining existing lectures

So what happens is the lecture comes in my activity_feed with a Join button option at the bottom...which should create a lecturerelationship of an "active" & "joinedlecture" (which obviously are supposed to be coming from the user & lecture classes. But the error i get when i click the join button is as follows:

ActiveRecord::StatementInvalid in LecturerelationshipsController#create

SQLite3::ConstraintException: constraint failed: INSERT INTO "lecturerelationships"     ("active_id", "created_at", "joinedlecture_id", "updated_at") VALUES (?, ?, ?, ?)

Also i've included my user model (seems the error is referring to it) user.rb

class User < ActiveRecord::Base
  attr_accessible :email, :name, :password, :password_confirmation
  has_secure_password
  has_many :lectures, :dependent => :destroy


  has_many :lecturerelationships, :foreign_key => "active_id", :dependent => :destroy
  has_many :joined_lectures, :through => :lecturerelationships, :source =>    :joinedlecture

  before_save { |user| user.email = email.downcase }
  before_save :create_remember_token

  validates :name, :presence => true, :length => { :maximum => 50 }
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  validates :email, :presence => true,
        :format => { :with => VALID_EMAIL_REGEX },
        :uniqueness => { :case_sensitive => false }
  validates :password, :presence => true, :length => { :minimum => 6 }
  validates :password_confirmation, :presence => true

  def activity
    # This feed is for "My Activity" - basically lectures i've started
    Lecture.where("user_id = ?", id)
  end

  def friendactivity
     Lecture.from_users_followed_by(self)
  end

  # lECTURE TO USER (JOINING) RELATIONSHIPS
  def joined?(selected_lecture)
    lecturerelationships.find_by_joinedlecture_id(selected_lecture.id)
  end

  def join!(selected_lecture)
    lecturerelationships.create!(:joinedlecture_id => selected_lecture.id)
  end

  def exit!(selected_lecture)
   lecturerelationships.find_by_joinedlecture_id(selected_lecture.id).destroy
  end


end

Thanks for any and all help - i'll be on here for a while so as mentioned i'd GREATLY appreciate someone who may have the time to work through my issues with me...

Answer 1

I would start with the following models, using Enrollment for the membership table.
Class naming is critical for this.

class User < ActiveRecord::Base
  has_many :enrollments
  has_many :users, :through => :enrollments
end

class Lecture < ActiveRecord::Base
  has_many enrollments
  has_many users, :through => :enrollments
end

class Enrollment < ActiveRecord::Base
  belongs_to :user
  belongs_to :lecture
end

The main trick to rails is using the right names and following the conventions and letting the framework do most of the work for you. Step off the path and the errors can be endless and the code gets messy quickly :)

Answer 2

It looks like your _join.html.erb uses build to form a new lecturerelationships association and then the join! call uses create to make another one on the same object. My guess is that the second call interrupts a transaction started by the first one and that's why you are getting the database is locked: commit transaction error.

I think it is considered good practice to keep this sort of code out of your views.