How do I add a HABTM record in CakePHP? - cakephp

Question

I am new to CakePHP and have a fairly basic question.
I have two tables : books and users. books and users have a habtm relationship. I have created the MVC for the above.
Now when a user logs into the system, I want the user to be able to reserve a book (ie an entry in books_users), by looking at the results of the 'index' action. What is the API to be used?
$this->Book->save() does not seem appropriate as we aren't creating a book. We only want an association between an existing book and the logged-in user.
I am trying to avoid, retrieving $this->Book, iterating manually through the sub-array User, creating a new sub-array and saving the whole thing back. I am sure there must be a simpler way.

Answer 1

Adapted from Chuck's answer, unsure why edit was pushed back.
In app/Model/Book.php
class Book extends AppModel {
/************************************************************************
* If you want your multiple assoc. to work you must set unique to *
* false, otherwise when you save an entry it will enforce unique *
* on book ID and subsequently your associations will delete previously *
* saved associations, acting more like "User HasMany Books". *
************************************************************************/
var $hasAndBelongsToMany = array(
'User' => array(
'className' => 'User',
'unique' => false
));
public function addUser($bid, $uid) {
$this->data['User']['id'] = $uid;
$this->data['Book']['id'] = $bid;
$this->save($this->data);
}
}
In app/Controller/BooksController.php (or UsersController)
$this->Book->addUser($bid, $uid);
Fat Models / Skinny Controllers. Allows duplicate entries (you need to constrain limits and check for duplicates, otherwise default behaviour makes HMBTM difficult). Does exactly what you want it to, you just need to supply book and user id.
CakePHP doesn't tend to encourage complex associations, and the reason this is because HMBTM is just a convenience and care should be taken when mixing it with other associations, as per the link provided below, self defined associations are more predictable than HMBTM in CakePHP
http://book.cakephp.org/2.0/en/models/saving-your-data.html#what-to-do-when-habtm-becomes-complicated

Answer 2

You simply need to save a record to Book or User that contains the ids of both and it will insert it into the HABTM table.
$this->data['User']['id'] = {USER_ID};
$this->data['Book']['id'] = {BOOK_ID};
$this->Book->save($this->data);
Look at the HABTM table and you will find the record.

Answer 3

did you bake your application? This (basic) functionality will be provided to you for you to adapt.
In short - take the id of the book and the id of the user. Save it to your books_users table.
id | book_id | user_id
1 1 1
2 2 2
3 2 3
If you have set your associations up correctly, when you request a user, all their books will be returned from the join table.
Your logic will need to deal with - number of books available,if a person can reserve more than one book at once...
http://book.cakephp.org/2.0/en/models/saving-your-data.html#saving-related-model-data-habtm
Has an example.