Hi all.
I'm trying to get my head around HABTM associations with extra fields
in the join table, but without much success.
So, its confessional debugging time :-) I'm using latest stable
release of Cake 1.2.6.
Here's what I have so far...
My understanding is that if I want to use additional fields in the
join table (PostsTag), I have to specify the HABTM relationship by
hand:
class Post extends AppModel {
var $hasMany = array(
"PostsTag"
);
}
class Tag extends AppModel {
var $hasMany = array(
"PostsTag"
);
}
class PostsTag extends AppModel {
var $belongsTo = array(
"Post",
"Tag"
);
}
My Post data entry form looks like this (form.ctp):
<?php echo $form->create("Post", array("action"=>$this->action)) ?>
<?php echo $form->input("Post.id") ?>
<?php echo $form->input("Post.name") ?>
<?php echo $form->input("PostsTag.0.tag_id")?>
<?php echo $form->input("PostsTag.0.weight")?>
<?php echo $form->end("Submit") ?>
<?php echo pr($this->data) ?>
My add method in the posts controller looks like this:
function add() {
if (!empty($this->data)) {
if ($this->Post->saveAll($this->data)) {
$this->Session->setFlash("Saved");
}
else {
$this->Session->setFlash("Error");
}
}
$this->_populateLookups();
$this->render("form");
}
_populateLookups() is a helper function that sets the view variable to
populate the drop down for tags:
function _populateLookups() {
$tags = $this->Post->PostsTag->Tag->find("list");
$this->set(compact("tags"));
}
The edit action in PostsController looks like this:
function edit($id) {
if (!empty($this->data)) {
if ($this->Post->saveAll($this->data)) {
$this->Session->setFlash("Saved");
}
else {
$this->Session->setFlash("Error");
}
}
else {
$this->data = $this->Post->read(null, $id);
}
$this->_populateLookups();
$this->render("form");
}
Adding a new post and tagging it with a weight works fine.
However, updating an existing post creates duplicate key violations
(their is a unique key on post_id, tag_id in the posts_tags model)
because cake doesn't remove the join table rows as it does if you use
$hasAndBelongsToMany
Now, I could add some code before $this->Post->save($this->data) to
remove any PostsTag with the same post_id, but what if the save()
fails? All the habtm join data will have been lost :-(
How do I get cake to remove the join table data when it saves the post
like it does when you use a hasAndBelongsToMany relationship in the
model?
tbh, this information should be in the cake book (there's a request in
the comments of the habtm pages for it). Once I have a satisfactory
answer I'll add it :-)
Check out the new CakePHP Questions site http://cakeqs.org and help others with
their CakePHP related questions.
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