[Ruby On Rails] belongs_to with :class_name option fails.

Question

I have no idea what went wrong but I can't get belongs_to work with :class_name option. Could somebody enlighten me. Thanks a lot!

Here is a snip from my code.

class CreateUsers < ActiveRecord::Migration
    def self.up
        create_table :users do |t|
            t.text :name
        end
    end

    def self.down
        drop_table :users
    end
end

#####################################################

class CreateBooks < ActiveRecord::Migration
    def self.up
        create_table :books do |t|
            t.text :title
            t.integer :author_id, :null => false
        end
    end

    def self.down
        drop_table :books
    end
end

#####################################################

class User < ActiveRecord::Base
    has_many: books
end

#####################################################

class Book < ActiveRecord::Base
    belongs_to :author, :class_name => 'User', :validate => true
end

#####################################################

class BooksController < ApplicationController
    def create
        user = User.new({:name => 'John Woo'})
        user.save
        @failed_book = Book.new({:title => 'Failed!', :author => @user})
        @failed_book.save # missing author_id
        @success_book = Book.new({:title => 'Nice day', :author_id => @user.id})
        @success_book.save # no error!
    end
end

environment:

ruby 1.9.1-p387 Rails 2.3.5

Answer 1

Try removing t.integer :author_id, :null => false from your CreateBooks Migration. belongs_to will create the association automatically.

Answer 2

It should be

belongs_to :user, :foreign_key => 'author_id'

if your foreign key is author id. Since you actually have User class, your Book must belong_to :user.

Answer 3

class User < ActiveRecord::Base
  has_many :books, :foreign_key => 'author_id'
end

class Book < ActiveRecord::Base
  belongs_to :author, :class_name => 'User', :foreign_key => 'author_id', :validate => true
end

The best thing to do is to change your migration and change author_id to user_id. Then you can remove the :foreign_key option.

Answer 4

Thanks for all your helps. I am very appreciated!

@Tony Fontenot, @Evgeny Shadchnev: As for the suggestion of using :user instead, it is in fact more than a reference to the User class, there is another field created_by which is another User instance who put the entry into the application like the following code:

belongs_to :author, :class_name => 'User', :validate => true
belongs_to :creator, :class_name => 'User', :validate => true

In fact, I have tried to add a :foreign_key option as well but it didn't help. My Code was:

belongs_to :author, :class_name => 'User', :foreign_key => 'author_id', :validate => true
belongs_to :creator, :class_name => 'User', :foreign_key => 'author_id', :validate => true

Have I missed something?

@kingjeffrey: I did try to remove the NOT NULL in the database and in the asscoiation of the User model. Unfortunately, it resulted null for author_id and creator_id fields. :(