How to get different values ​​using isl / relational and has_many algebra: via

Question

When I try to display all the films in which a person is located, and they have more than 1 role (director, writer, actor) in the film, I get a few lines for this film. If I add .select ("DISTINCT id") or movies. * To try to eliminate duplicates, I get the following error:

Mysql2 :: Error: you have an error in the SQL syntax; check the manual that matches your version of MySQL server for the correct syntax to use next to DISTINCT id FROM moviesINNER JOIN movie_peopleON movies.id = movie_peop' at line 1: SELECTmovies .*, DISTINCT id FROMmovies INNER JOINmovie_people ONmovies .id =movie_people .movie_id WHERE ((movie_people`.person_id = 601619)) ORDER BY title LIMIT 18 OFFSET 0

I do not know how to correctly encode an isl request. Please, help.
Thank.

application / controllers

class PeopleController < ApplicationController  
def show  
    @person = Person.find(params[:id])  
    @movies = @person.movies.select('DISTINCT id').
      paginate :per_page => 18, :page => params[:page],
               :order => sort_order(params[:sort]) 
end  

application / models

class Person < ActiveRecord::Base  
  has_many :movie_people  
  has_many :movies, :through => :movie_people  
end  

class MoviePerson < ActiveRecord::Base  
  belongs_to :movie  
  belongs_to :person  
end  

class Movie < ActiveRecord::Base  
  has_many :movie_people  
  has_many :people, :through => :movie_people  
end  

db / schema.rb

  create_table "people", :force => true do |t|  
    t.string   "name"  
  end  

  create_table "movie_people", :force => true do |t|  
    t.integer  "movie_id"  
    t.integer  "person_id"  
    t.integer  "role"  
  end  

  create_table "movies", :force => true do |t|  
    t.string   "title"  
    t.string   "year"  
  end  

movies / show.html.erb

Title:<%= @movie.title %><br>
Year:<%= @movie.year %><br>
<% @movie.movie_people.group_by(&:role).each do |r, a| %>  
 <%= %w(Director: Writer: Cast:)[r] %>  
  <% a.each do |c| %>  
   <%= link_to c.person.name, 
       :controller => 'people', :action => 'show', :id => c.person.id %>
  <% end %><br>  
<% end %>  

Title: Fahrenheit 9/11
Release year: 2004
Director: Michael Moore
Writer: Michael Moore
Cast: Michael Moore George W. Bush

people / show.html.erb

Name:<%= @person.name %>
<% @movies.each do |movie| %>  
<br><%= link_to movie.title, movie %> (<%= movie.year %>)  
<% end %>  

:
9/11 (2004)
9/11 (2004)
9/11 (2004)

Answer 1

Arel, uniq select distinct SQL. , Arel has_many, () -

@person.movies.uniq

. http://apidock.com/rails/ActiveRecord/QueryMethods/uniq Rails Arel,

Answer 2

, Rails.

, , :

@person.movies.except(:select).select('DISTINCT id')

Answer 3

- rails - : select (distinct) : has_many: SQL

has_many :movies, :through => :movie_people, :select => 'distinct movies.*'