Question

What doesn’t work

On update form, if i change checkbox values, these habtm values don’t get saved to database.

Althought in create and update form i use the same method: $this->Employee->save($this->data) which should automatically handle HABTM data.

What works

I`v sucessfully set up HABTM Model by following this tutorial: Employees hasAndBelongsToMany Languages (i.e to specify which employee speaks which language).

I can create the relations: when creating new employee with create form, check any languages which employee knows and it sucessfully saves to database: employee goes to employee database table, language to language and the relations goes to employee_language table.

On edit form, i see which checboxes i checked while creating employee.

What i’v found to (probably) be guilty

When evaluating what data goes to database while creating and updating employee, i’v found out that $this->data variable structure differs.

On create form (check 2 languages):

"$this->data"   Array [2]   
    Employee    Array [6]   
        name_lv John Doe    
        position_lv Computer administrator  
        enabled 0       
    Language    Array [1]   
        Language    Array [2]   
            0   1   
            1   5   

On update form (checked additional language, so 3 languages):

"$this->data"   Array [1]   
    Employee    Array [8]   
        name_lv John Doe    
        position_lv Computer administrator  
        Language    Array [3]   
            0   1   
            1   5   
            2   4   
        enabled 0   
        id  68  

Note that Languages are now accessable under $this->data["Employee"]["Language"] not like when creating $this->data["Language"]

Workaround

If i do $this->data["Language"] = $this->data["Employee"]["Language"]; then values get saved (yay), except that duplicate entries are present in employee_language HABTM table (oh no).

So which switch do i switch to make my checkboxes updateable?

More details (if you will)

(model) employee.php

class Employee extends AppModel {
  var $name = "Employee";

  var $hasAndBelongsToMany = array (
    "Language" =>
        array(
            "className"     => "Language",
            "conditions"    => array(
                "Language.enabled" => "1"
            )
        )
  );
  ...
}

(model) language.php:

class Language extends AppModel {

  var $name = "Language";
  ...
}

(view) admin_create.ctp (this is create form. This snippet renders checkboxes for all available languages):

...
<?php  
    echo $form->input('Language',array(
        'label' => 'Speaks in languages:',
        'type' => 'select',
        'multiple' => 'checkbox',
        'options' => $languages
));  ?>
...

(view) admin_update.ctp (I can see which languages i checked while creating employee):

...
<?php  
    echo $form->input('Language',array(
        'label' => 'Speaks in languages:',
        'type' => 'select',
        'multiple' => 'checkbox',
        'options' => $languages,
        'selected' => $html->value('Employee.Language')
));  ?>
...

Answer 1

Mark provided an answer in comments that solves the problem:

… you dont need to and you shouldnt use “selected” in your form
input array.

Yes, when i removed “selected” property, then suddenly i was able to do UPDATE on HABTM data.
So now my input control looks like:

<?php  
    echo $form->input('Language',array(
        'label' => 'Speaks in languages:',
        'type' => 'select',
        'multiple' => 'checkbox',
        'options' => $languages
));  ?>

Not having a way to convert comment as an answer, trying to contact @mark to post his comment as an answer, but no actions has taken, i’m answering my own question so that others can see that this question has a solution. That’s what is suggested on meta: https://meta.stackexchange.com/questions/1555/mark-a-comment-as-answer-to-a-question/1558#1558