ActiveRecord calculations with joins on renamed foreign keys?

rubyonrails-talk
1

Hi,

Could someone please explain to me how to do use the ActiveRecord helpers to do calculations with joins on renamed foreign keys?

My situation:

User Model: has_many :books

Book Model: belongs_to :created_by,               :class_name => 'User',               :foreign_key => 'created_by'

I'm trying to calculate a list of the users by summed book scores, with the following code.

@users = User.sum('books.score', :include => 'books')

I'm getting the error: 42S22Unknown column 'books.user_id' in 'on clause'. Isn't Rails supposed to be smart enough to realize that the foreign key has been renamed? How do I tell it to use created_by as the foreign key here?

Thanks, R

2

rbibby wrote:

Hi,

Could someone please explain to me how to do use the ActiveRecord helpers to do calculations with joins on renamed foreign keys?

My situation:

User Model: has_many :books

Book Model: belongs_to :created_by,               :class_name => 'User',               :foreign_key => 'created_by'

I'm trying to calculate a list of the users by summed book scores, with the following code.

@users = User.sum('books.score', :include => 'books')

I'm getting the error: 42S22Unknown column 'books.user_id' in 'on clause'. Isn't Rails supposed to be smart enough to realize that the foreign key has been renamed? How do I tell it to use created_by as the foreign key here?

Show us your schema/migrations.

3

Here you go...

class CreateUsers < ActiveRecord::Migration   def self.up     create_table "users", :force => true do |t|       t.column :login, :string       t.column :email, :string       t.column :crypted_password, :string, :limit => 40       t.column :salt, :string, :limit => 40       t.column :created_at, :datetime       t.column :updated_at, :datetime       t.column :remember_token, :string       t.column :remember_token_expires_at, :datetime       t.column :activation_code, :string, :limit => 40       t.column :activated_at, :datetime       t.column :admin_flag, :integer     end   end

end

class CreateBooks < ActiveRecord::Migration

  def self.up     create_table :books do |t|       t.column :title, :string       t.column :description, :text       t.column :score, :integer, :default => 0       t.column :created_at, :timestamp       t.column :created_by, :integer

    end

  end

end

4

What happens when you do this?:

@users = User.sum('book.score', :include => 'books')

5

Mysql::Error: #42S02Unknown table 'book' in field list: SELECT sum(book.score) AS sum_book_score FROM users LEFT OUTER JOIN books ON books.user_id = users.id ORDER BY score desc

6

Try it like this:

User Model: has_many :books, :foreign_key => "created_by"

7

It works! Thank you so much! So is the key that the foreign key needs to be specified on both sides of the association? Is the books model being done correctly as is?

Thanks again, R

8

rbibby wrote:

It works! Thank you so much! So is the key that the foreign key needs to be specified on both sides of the association? Is the books model being done correctly as is?

Thanks again, R

Yeah apparently it does, though the examples in AWDR don't do it that way for some reason.

For the Book model you can try:

book = Book.find(1) book.user

and it should give you back the user for that book.