[ci skip] correct for ActiveRecord::Associations::Preloader

[aditya-kapoor]

I saw this example and something doesn't seemed right.

[senny]

@aditya-kapoor please use the PR body to explain the change. I'm not sure I understand why i'ts necessary. As far as I can tell the example only use the has_many :books association. The inverse is not mentioned.

[aditya-kapoor]

@senny I think there the belongs_to is missing in the example code.

If there was no belongs_to then query specified in the next lines Author.includes(:books).where(:name => ['bell hooks', 'Homer').to_a would not work.

Please correct if I am missing something.

[senny]

@aditya-kapoor why should it not work?

# Activate the gem you are reporting the issue against.
require 'active_record'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :authors do |t|
    t.string :name
    t.integer :age
  end

  create_table :books do |t|
    t.string :title
    t.integer :sales
    t.belongs_to :author
  end
end

class Author < ActiveRecord::Base
  # columns: name, age
  has_many :books
end

class Book < ActiveRecord::Base
  # columns: title, sales
end

class ExampleTest < Minitest::Test
  def test_example
    Author.includes(:books).where(name: ['bell hooks', 'Homer']).to_a

    Author.includes(:books).where(books: {title: 'Illiad'}).to_a
  end
end

# == OUTPUT
# -- create_table(:authors)
# D, [2015-06-23T15:50:44.702986 #23785] DEBUG -- :    (7.6ms)  CREATE TABLE "authors" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar, "age" integer)
#    -> 0.0184s
# -- create_table(:books)
# D, [2015-06-23T15:50:44.703782 #23785] DEBUG -- :    (0.2ms)  CREATE TABLE "books" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "title" varchar, "sales" integer, "author_id" integer)
#    -> 0.0006s
# Run options: --seed 34140

# # Running:

# D, [2015-06-23T15:50:44.813255 #23785] DEBUG -- :   Author Load (0.1ms)  SELECT "authors".* FROM "authors" WHERE "authors"."name" IN ('bell hooks', 'Homer')
# D, [2015-06-23T15:50:44.837158 #23785] DEBUG -- :   SQL (0.2ms)  SELECT "authors"."id" AS t0_r0, "authors"."name" AS t0_r1, "authors"."age" AS t0_r2, "books"."id" AS t1_r0, "books"."title" AS t1_r1, "books"."sales" AS t1_r2, "books"."author_id" AS t1_r3 FROM "authors" LEFT OUTER JOIN "books" ON "books"."author_id" = "authors"."id" WHERE "books"."title" = ?  [["title", "Illiad"]]
# .

# Finished in 0.044347s, 22.5494 runs/s, 0.0000 assertions/s.

# 1 runs, 0 assertions, 0 failures, 0 errors, 0 skips

[aditya-kapoor]

@senny Usually it is the has_many and belongs_to arrangement which we have.
We don't have any knowledge of author_id inside the Book model. See the columns comment inside Book model.

PS you are explicitly specifying this in your migration, so why not in your model?

[senny]

@aditya-kapoor granted, the columns: comment could be extend with author_id. There's still no need for the belongs to though. I feel like this makes it more explicit what we are talking about. It's only related to the has_many and of course the right table layout.

[senny]

Merged a modified version only expanding the columns: comment: (de0a2a4)

[aditya-kapoor]

@senny Thank you for your time and explanation.

[senny]

@aditya-kapoor thanks for being persistent and help us improve the docs ✨