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Asked: 2026-06-10T18:16:05+00:00

models: class Person < ActiveRecord::Base attr_accessible :email, :first, :last, :uuid, :books has_many :books end

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models:

class Person < ActiveRecord::Base
  attr_accessible :email, :first, :last, :uuid, :books
  has_many :books
end

class Book < ActiveRecord::Base
  belongs_to :person
  attr_accessor :blurb, :published, :title, :person
  attr_accessible :person
end

I created a Person using the Rails 3.2.8 console like this:

person = Person.create!( {:first => "John", :last => "Doe"} )

and then created a Book

book = Book.create!( {:title => "Ruby for Dummies"} )

I then try to associate them like this:

person.books << book

When I query the person for books, I get an array with the book I created, but when I query the book for the person it belongs to, I get nil. I expected to get the person, given that all information was persisted (I see the SQL commands and I checked the database and the data is correct, i.e. the row in the book table points back to the person id it should.)

What am I missing?

thanks

Edit- Schema:

CREATE TABLE `persons` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `first` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
    `last` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
    `uuid` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
    `email` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
    `created_at` DATETIME NOT NULL,
    `updated_at` DATETIME NOT NULL,
    PRIMARY KEY (`id`)
)
COLLATE='utf8_unicode_ci'
ENGINE=InnoDB
AUTO_INCREMENT=2;

CREATE TABLE `books` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `title` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8_unicode_ci',
    `blurb` TEXT NULL COLLATE 'utf8_unicode_ci',
    `published` TINYINT(1) NULL DEFAULT NULL,
    `person_id` INT(11) NULL DEFAULT NULL,
    `created_at` DATETIME NOT NULL,
    `updated_at` DATETIME NOT NULL,
    PRIMARY KEY (`id`)
)
COLLATE='utf8_unicode_ci'
ENGINE=InnoDB
AUTO_INCREMENT=3;
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1 Answer

  1. Editorial Team

    Assuming your migrations are correct, there is nothing wrong with your code which should produce the following results:

    1.9.3p194 :001 > person = Person.create!( {:first => "John", :last => "Doe"} )
   (0.1ms)  begin transaction
  SQL (145.9ms)  INSERT INTO "people" ("book_id", "created_at", "email", "first", "last", "updated_at", "uuid") VALUES (?, ?, ?, ?, ?, ?, ?)  [["book_id", nil], ["created_at", Mon, 03 Sep 2012 21:35:53 UTC +00:00], ["email", nil], ["first", "John"], ["last", "Doe"], ["updated_at", Mon, 03 Sep 2012 21:35:53 UTC +00:00], ["uuid", nil]]
   (43.5ms)  commit transaction
 => #<Person id: 1, email: nil, first: "John", last: "Doe", uuid: nil, book_id: nil, created_at: "2012-09-03 21:35:53", updated_at: "2012-09-03 21:35:53"> 
1.9.3p194 :005 > book = Book.create!( {:title => "Ruby for Dummies"} )
   (0.1ms)  begin transaction
  SQL (1.4ms)  INSERT INTO "books" ("blurb", "created_at", "person_id", "published", "title", "updated_at") VALUES (?, ?, ?, ?, ?, ?)  [["blurb", nil], ["created_at", Mon, 03 Sep 2012 21:36:25 UTC +00:00], ["person_id", nil], ["published", nil], ["title", nil], ["updated_at", Mon, 03 Sep 2012 21:36:25 UTC +00:00]]
   (4.4ms)  commit transaction
 => #<Book id: 1, blurb: nil, published: nil, title: nil, person_id: nil, created_at: "2012-09-03 21:36:25", updated_at: "2012-09-03 21:36:25"> 
1.9.3p194 :006 > person.books << book
   (0.1ms)  begin transaction
   (0.3ms)  UPDATE "books" SET "person_id" = 1, "updated_at" = '2012-09-03 21:36:39.566387' WHERE "books"."id" = 1
   (4.4ms)  commit transaction
  Book Load (0.3ms)  SELECT "books".* FROM "books" WHERE "books"."person_id" = 1
 => [#<Book id: 1, blurb: nil, published: nil, title: nil, person_id: 1, created_at: "2012-09-03 21:36:25", updated_at: "2012-09-03 21:36:39">] 
1.9.3p194 :007 > Book.all
  Book Load (0.5ms)  SELECT "books".* FROM "books" 
 => [#<Book id: 1, blurb: nil, published: nil, title: nil, person_id: 1, created_at: "2012-09-03 21:36:25", updated_at: "2012-09-03 21:36:39">]

    The problem is with your Book model, try the following:

    class Book < ActiveRecord::Base
  attr_accessible :person, :title, :person

  belongs_to :person
end

    Before:

    1.9.3p194 :002 > Book.last
  Book Load (0.1ms)  SELECT "books".* FROM "books" ORDER BY "books"."id" DESC LIMIT 1
 => #<Book id: 4, blurb: nil, published: nil, title: nil, person_id: 1, created_at: "2012-09-03 21:55:33", updated_at: "2012-09-03 21:55:33"> 
1.9.3p194 :003 > Book.last.person
  Book Load (0.2ms)  SELECT "books".* FROM "books" ORDER BY "books"."id" DESC LIMIT 1
 => nil

    After:

    1.9.3p194 :001 > Book.last
  Book Load (0.4ms)  SELECT "books".* FROM "books" ORDER BY "books"."id" DESC LIMIT 1
 => #<Book id: 4, blurb: nil, published: nil, title: nil, person_id: 1, created_at: "2012-09-03 21:55:33", updated_at: "2012-09-03 21:55:33"> 
1.9.3p194 :002 > Book.last.person
  Book Load (1.0ms)  SELECT "books".* FROM "books" ORDER BY "books"."id" DESC LIMIT 1
  Person Load (0.1ms)  SELECT "people".* FROM "people" WHERE "people"."id" = 1 LIMIT 1
 => #<Person id: 1, email: nil, first: "John", last: "Doe", uuid: nil, created_at: "2012-09-03 21:48:02", updated_at: "2012-09-03 21:48:02">
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