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PORails 4 - trouble with two associations, same model
 

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    <p>I'm trying to make a simple movie database using Rails 4.0.0 as a learning project. I'm particularly interested in using scaffolding as much as possible, as this is one of the features that drew me to RoR in the first place.</p> <p>Yes, I do realize the <a href="http://ruby.railstutorial.org/book/ruby-on-rails-tutorial#cha-beginning" rel="nofollow noreferrer">potential risks</a> (Box 1.2.Scaffolding: Quicker, easier, more seductive), but I promise I won't have my project go public before I <em>really</em> understand what's going on beneath the hood. Right now I'm more in "evaluating technologies for my next super duper project"-mode.</p> <p>Here's what I've got so far:</p> <pre><code>rails g scaffold Person name:string rails g scaffold Movie name:string </code></pre> <p>Now, I could've done something like</p> <pre><code>rails g scaffold Movie name:string person_id:integer </code></pre> <p>instead, but I want a movie to be associated with both a director and an actor. (Next step is to make an association that relates multiple actors to a single movie, but I'm not quite there yet.)</p> <p>So, I headed over to the blog post <a href="http://www.spacevatican.org/2008/5/6/creating-multiple-associations-with-the-same-table/" rel="nofollow noreferrer">Creating Multiple Associations With the Same Table</a>, describing pretty much what I need. It's a somewhat old post, so things might have changed now - I don't know. Anyway. This how I changed the models:</p> <pre><code>class Person &lt; ActiveRecord::Base has_many :movies end </code></pre> <p>and</p> <pre><code>class Movie &lt; ActiveRecord::Base belongs_to :director_id, :class_name =&gt; 'Person', :foreign_key =&gt; 'person_id' belongs_to :actor_id, :class_name =&gt; 'Person', :foreign_key =&gt; 'actor_id' end </code></pre> <p>and finally the magical</p> <pre><code>rake db:migrate </code></pre> <p>Starting the WEBrick by running <code>rails s</code> in the console, I open my browser and start registering people</p> <p><img src="https://i.stack.imgur.com/VF2Os.png" alt="enter image description here"></p> <p>The time has come to start registering movies. According to previous questions <a href="https://stackoverflow.com/questions/8420769/rails-how-to-migrate-a-database-where-i-added-a-belongs-to-relationship">here</a> and <a href="https://stackoverflow.com/questions/4619651/how-to-reflect-in-the-database-a-new-belongs-to-and-has-many-relationship-in-rub">here</a> I have to make a migration script in order to create the necessary database fields. So this is what I did:</p> <pre><code>rails g migration AddPersonIdsToMovies director_id:integer actor_id:integer </code></pre> <p>I also updated the <code>app/views/movies/_form.html.erb</code> to </p> <pre><code>&lt;%= form_for(@movie) do |f| %&gt; &lt;% if @movie.errors.any? %&gt; &lt;div id="error_explanation"&gt; &lt;h2&gt;&lt;%= pluralize(@movie.errors.count, "error") %&gt; prohibited this movie from being saved:&lt;/h2&gt; &lt;ul&gt; &lt;% @movie.errors.full_messages.each do |msg| %&gt; &lt;li&gt;&lt;%= msg %&gt;&lt;/li&gt; &lt;% end %&gt; &lt;/ul&gt; &lt;/div&gt; &lt;% end %&gt; &lt;div class="field"&gt; &lt;%= f.label :name %&gt;&lt;br&gt; &lt;%= f.text_field :name %&gt; &lt;/div&gt; &lt;div class="field"&gt; &lt;%= f.label :director_id %&gt;&lt;br&gt; &lt;%= f.select :director_id, Person.all.collect {|x| [x.name, x.id]}, {}, :multiple =&gt; false %&gt; &lt;/div&gt; &lt;div class="field"&gt; &lt;%= f.label :actor_id %&gt;&lt;br&gt; &lt;%= f.select :actor_id, Person.all.collect {|x| [x.name, x.id]}, {}, :multiple =&gt; false %&gt; &lt;/div&gt; &lt;div class="actions"&gt; &lt;%= f.submit %&gt; &lt;/div&gt; &lt;% end %&gt; </code></pre> <p>When I create a new movie, the view shows up fine and the select inputs works fine. However, the data in the director and actor field isn't persisted. I ran <code>rails console</code> and looked at the newly created movie:</p> <pre><code>irb(main):004:0&gt; mov = Movie.first Movie Load (0.2ms) SELECT "movies".* FROM "movies" ORDER BY "movies"."id" ASC LIMIT 1 =&gt; #&lt;Movie id: 1, name: "No such movie", created_at: "2013-08-02 17:02:12", updated_at: "2013-08-02 17:02:12", director_id: nil, actor_id: nil&gt; </code></pre> <p>which is kind'a disappointing with no director or actor info.</p> <p><strong>Update</strong></p> <p>Based on @Mattherick's suggesition, I edited the private part of the <code>movies_controller.rb</code> to this:</p> <pre><code># Never trust parameters from the scary internet, only allow the white list through. def movie_params params.require(:movie).permit(:name, :director_id, :actor_id) end </code></pre> <p>Unfortunately, when I post a new movie I get</p> <blockquote> <p>Person(#70319935588740) expected, got String(#70319918738480)</p> <p>Extracted source: </p> <pre><code># POST /movies.json def create @movie = Movie.new(movie_params) respond_to do |format| if @movie.save </code></pre> </blockquote> <p>and the request data goes as </p> <p>{"utf8"=>"✓", "authenticity_token"=>"???", "movie"=>{"name"=>"Romantic Comedy", "director_id"=>"2", "actor_id"=>"1"}, "commit"=>"Create Movie"}</p> <p><strong>Update 2</strong></p> <p>I tried to create a new Movie in the rails console, like this:</p> <pre><code>irb(main):001:0&gt; movie = Movie.new(name: "My fine movie", director_id: "1", actor_id: "2") ActiveRecord::AssociationTypeMismatch: Person(#70311109773080) expected, got String(#70311102311480) </code></pre> <p>which is what you'd expect from the POST to the controller. This made me test what happened if I excluded the quotation marks for <code>director_id</code> and <code>actor_id</code>. So I did</p> <pre><code>irb(main):005:0&gt; movie = Movie.new(name: "My fine movie", director_id: 1, actor_id: 2) ActiveRecord::AssociationTypeMismatch: Person(#70282707507880) expected, got Fixnum(#70282677499540) </code></pre> <p>Still using the console, I decided to create an actor and a director</p> <pre><code>director = Person.new(name: "Woody Allen") director.save actor = Person.new(name: "Arnold Schwarzenegger") actor.save </code></pre> <p>and then I did</p> <pre><code>movie = Movie.new(name: "I'd like to see that", director_id: director, actor_id: actor) movie.save </code></pre> <p>which worked like a charm (output omitted for brevity). So the whole question boils down to <strong>"How can I pass a Person as the argument to <code>director_id</code> and <code>actor_id</code> through the web interface?"</strong> </p> <p>If I had a single field in Movies called <code>person_id: integer</code>, I believe that rails would've inferred that I'm not trying to pass a string containing the id of a person, but rather I'm trying to pass an entire person object.</p> <p><strong>Update 3</strong></p> <p>I tested my suspicion that rails understands how to deal with posts when the foreign key column is named after the pattern [table]_id. So I created a new project with a <code>Continent</code> model and a <code>Country</code> model, where <code>rails g scaffold Country name:string continent_id:integer</code>. I changed my <code>Country</code> view to include</p> <pre><code>&lt;div class="field"&gt; &lt;%= f.label :continent_id %&gt;&lt;br&gt; &lt;%= f.select :continent_id, Continent.all.collect {|x| [x.name, x.id]} %&gt; &lt;/div&gt; </code></pre> <p>instead of the default numeric field. The <code>continent_id</code> is still posted a string:</p> <pre><code>Started POST "/countries" for 127.0.0.1 at 2013-08-03 10:40:40 +0200 Processing by CountriesController#create as HTML Parameters: {"utf8"=&gt;"✓", "authenticity_token"=&gt;"???", "country"=&gt;{"name"=&gt;"Uganda", "continent_id"=&gt;"4"}, "commit"=&gt;"Create Country"} </code></pre> <p>yet rails understood that <code>continent_id</code> was the identifier of an entry in the <code>Continent</code> table.</p> <p>Sadly, the inferrer mechanism doesn't work in my original case, as I have two associations from <code>Movie</code> to the <code>Person</code> table. I need to somehow make sure rails understand that there is a mapping from <code>director_id</code> to a <code>Person</code>.</p> <p><strong>Update 4</strong></p> <p>According to some sources, it seems as I need to refine the <code>Person</code> model further. So I did</p> <pre><code>class Person &lt; ActiveRecord::Base has_many :directed_movies, :class_name =&gt; 'Movie', :foreign_key =&gt; 'director_id' has_many :acted_movies, :class_name =&gt; 'Movie', :foreign_key =&gt; 'actor_id' end </code></pre> <p>but still not fixing my problems.</p> <p>I'm kind'a lost. <del>Can anyone give me a few pointers on what I'm missing here?</del> Can anyone help me map from <code>director_id</code> to <code>person_id</code>? Thanks!</p>
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    1. COYou have to add `accepts_nested_attributes_for :actor` and the same for director in the Movie model ;)
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    2. COI think that you should use has_and_belongs_to_many relation, because movie has many actors and actor can appear in many movies
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      1. USBerlin
    3. COWhich parameters do you get in your controller? Are you on rails 4? You also have to update your private method in your rails controller..in rails 4 only permitted parameters are allowed. @MrYoshiiji I don't think accepts_nested_attributes are necessary..
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