Question about saving associations when using has_many :thro

I’ve got a User model and a Book model. A user is required to submit
books each month to be reviewed by other users. I have the following
relationships defined:

the join model

belongs_to :user
belongs_to :book


each book is reviewed by many users. This allows us to get the


objects associated with this book

has_many :book_reviews, :dependent => true

this :through association allows us to retrieve the users who have

been assigned to review this book

has_many :reviewing_users, :through => :book_reviews, :source => :user

each book is submitted by a single user

belongs_to :user


each user must submit a number of books each month

has_many :submitted_books, :class_name => “Book”, :dependent =>

each user has a list of books that they are required to review

has_many :book_reviews, :dependent => true

this :through association allows us to retrieve the books the user

is required to review

has_many :books_to_review, :through => :book_reviews, :source => :book

Now, when a user submits a book, I must assign the book to be reviewed
by 5 different users. I’ve created an after_save callback in book.rb
which does the following:

users.each do |user|
  user.books_to_review << self!

unfortunately, when I add a new book model to the list of
books_to_review, it doesn’t actually insert the book model into the
book_reviews table. I can of course do the following instead:

users.each do |user|
book_review =“book_id” =>
user.book_reviews << book_review!

I was hoping that rais would be smart enough in the first case to add
a new book record to the book_reviews table, filling in the book_id
and user_id parameters, but instead it doesn’t even save it. I can,
however, print out the contents of user.books_to_review and sure
enough, it contains the new book that I’ve added, but I just can’t
figure out how to get rails to save this information to the table.

Can anyone tell me why rails isn’t saving the books_to_review list to
the user model in the first example? And how I can fix it? (or should
I just rely on using the second method instead?)



P.S. here is the schema for the book_reviews table:

| Field | Type | Null | Key | Default | Extra |
| id | int(11) | NO | PRI | | auto_increment |
| book_id | int(11) | YES | | | |
| user_id | int(11) | YES | | | |
| total_score | int(11) | YES | | | |
| created_at | datetime | YES | | | |
| updated_at | datetime | YES | | | |
| reviewed_at | datetime | YES | | | |