Question

Hello I’m making a form for establishing many-to-many relationship between two models

using this solution

I Have Three Model

Artist, Article, ArtistRelationship.

This is Artist Model.

 class Artist < ActiveRecord::Base
   default_scope order('created_at DESC')

   attr_accessible :body_en, :body_kr, :title_en, :title_kr

   has_many :articles, :through => :artist_relationships
   has_many :artist_relationships
 end

And this is Article Model.

 class Article < ActiveRecord::Base
    default_scope order('created_at DESC')

    attr_accessible :title, :body, :date

    has_many :artists, :through => :artist_relationships
    has_many :artist_relationships

 end

And this is ArtistRelationship Model

 class ArtistRelationship < ActiveRecord::Base
   default_scope order('created_at DESC')

   attr_accessible :article_id, :artist_id

   belongs_to :artist
   belongs_to :article

 end

Now I have a form for an article to set the artists.

 <%= form_for [:admin, article] do |f| %>
   .....
     <% Artist.all.each do |artist| %>
        <div>
           <%= label_tag :artist_ids, artist.title_kr %>
           <%= check_box_tag :artist_ids, artist.id, article.artists.include?(artist), :name => 'article[artist_ids][]' %>
        </div>
     <% end %>

The error come from here

 article.artists.include?(artist)

It raises these error

Mysql2::Error: Column ‘created_at’ in order clause is ambiguous: SELECT 1 AS one FROM artists INNER JOIN artist_relationships ON artists.id = artist_relationships.artist_id WHERE artist_relationships.article_id = 1 AND artists.id = 2 ORDER BY created_at DESC LIMIT 1

I can’t get what it means..

And weired thing occurs when I use pry to debug right above the code

 <%= check_box_tag :artist_ids, artist.id, article.artists.include?(artist), :name => 'article[artist_ids][]' %>

in pry console when I directly call article.artists.include?(artist)

It raise same error as I expected. but

When I call article.artists it returns an array of artist belongs to that article

then I call article.artists.include?(artist) again. I works fine.

What’s the problem of this?

Answer 1

in all your default scope, include the tableized version of the class

# article.rb
default_scope order('articles.created_at DESC')