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

score 66 · Answer 1 · answered Apr 21 '10 at 18:45

66

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.

answered Apr 21 '10 at 18:45

Tony Fontenot

5,091
1
21
19

7

I care about having good foreign keys. I wouldn't apply the suggestion about renaming the column, as it's clearer what's going on when the columns have the right name. – François Beausoleil Apr 21 '10 at 19:33
1

Either way works. Whatever makes sense for you and your team is the right thing to do. :) – Tony Fontenot Apr 21 '10 at 19:53
2

And to think that class_name: 'User' would have sufficed – Donato Mar 30 '15 at 21:25

score 8 · Answer 2 · answered Apr 21 '10 at 17:08

8

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.

answered Apr 21 '10 at 17:08

Evgeny Shadchnev

7,320
4
27
30

score 3 · Answer 3 · answered Jan 09 '18 at 15:23

I do in this way:

Migration -

class AddAuthorToPosts < ActiveRecord::Migration
  def change
    add_reference :posts, :author, index: true
    add_foreign_key :posts, :users, column: :author_id
  end
end

class Post

  belongs_to :author, class_name: "User"

score 3 · Answer 4 · answered Jul 24 '18 at 12:12

3

migration

t.belongs_to :author, foreign_key: { to_table: :users }

working on rails 5

answered Jul 24 '18 at 12:12

Lijun Guo

31
2

belongs_to with :class_name option fails

4 Answers4

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