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Background

Before I detail this method, I want to explain how I develop in cake without this program. Hopefully that will show you the true usefulness of the unbindValidation method. In every $validate property, for every field I plan on validating, I set a property called 'required'=>true for each field. Many new bakers don't understand what this does, so here is the lowdown. By default, cake sets every field in $validate to 'required'=>false. What this means is, if you want to validate the 'username' field, but for some reason it does not appear in $this->data, then Cake will skip validation on that field. So what? Well, here is how it can affect you...

When creating a new user account, I have a terms of service field called 'agree_to_tos'. If I don't set 'required'=>true for that field and merely leave it at the default (false), then the user can modify the form data before it is submitted and remove 'agree_to_tos' from the submitted form data. This means that if you performed isset($this->data['agree_to_tos']) it would return false. Thus, validation on the tos field is never performed, and assuming all other fields pass validation, a user is now created without having to agree to the terms of service! You can extrapolate this out to other scenarios which could potentially cause even harm to your site.

Let's say you decide to set all your fields to 'required'=>true beforehand in the $validate property. You could do this, but you'd run into trouble later when it came time to validate certain data and not other data... Here is an example:

In my UserModel::$validate property I have the following fields: 'username', 'nickname', 'password', 'password_confirm', 'newsletter', 'agree_to_tos', 'company_id', 'first_name', 'last_name'.

In my UsersController::add() method, I accept all of those fields but not 'first_name' or 'last_name' (I allow them to add it later during the ordering process or what not. I figure the less crap I ask users to provide during account creation, the more likely the are to create an account).

Now, lets say I set all fields in $validate to 'required'=>true. Well, validation would fail because 'first_name' and 'last_name' are required but not present. The solution would be to either 1) unset both fields from $validate; or 2) set 'required'=>false on both fields

Doing either is a hassle in my opinion because in some cases it might be more than 2 field that you want to modify, and there are other scenarios when you would want to list the fields you want to keep but not remove (examples below). It was for these reasons that I decided to write this method.

Explanation

This method will remove certain fields that you do not want from $validate and simultaneously set the remaining fields to 'required'. It also allows specifying an array of either the fields you want to keep, or the fields you want to remove. This can be useful in different situations. Here is how you use it:

#1: We can specifically remove fields from UserModel::$validate like this and simultaneously set the remaining fields to 'required'=>true
$this->User->unbindValidation('remove', array('first_name', 'last_name'), true);
#2: Or we can specify the fields we want to keep in UserModel::$validate and set as required (and automatically remove everything else):
$this->User->unbindValidation('keep', array('username', 'nickname', 'password', 'password_confirm', 'newsletter', 'agree_to_tos', 'company_id'), true);
Here are some other places I use it...

In my UsersController:edit() method, I don't require that users re-agree to the terms of service. This line takes care of that:
$this->User->unbindValidation('remove', array('agree_to_tos'), true);
In my UsersController::changeNickname() method, the only field I let users modify is 'nickname' and therefore this line takes care of that:
$this->User->unbindValidation('keep', array('nickname'), true);
So if you are already enticed then you can skip below to the code, but you may at least be wondering why not merely unset($this->User->validate['agree_to_tos'])? Well, that's fine, but what about in the nickname scenario? You will have to list every single field you want to unset, except for 'nickname'. You could of course set nickname to 'required'=>true, but if you decide to take that approach on a case-by-case basis, then when it comes time to save a bunch of fields (like 5 or more) you'll have to set required on each one... This is why having the parameter $type in the method is so handy. It lets you set $type='keep' and set the field to array('nickname') instead of listing every single field you want to remove! Also, you don't have to manually set each field you want to validate as 'required'=>true!

Code

(I prefer to place this in my app_model)

/**
 * Unbinds validation rules and optionally sets the remaining rules to required.
 * 
 * @param string $type 'Remove' = removes $fields from $this->validate
 *                       'Keep' = removes everything EXCEPT $fields from $this->validate
 * @param array $fields
 * @param bool $require Whether to set 'required'=>true on remaining fields after unbind
 * @return null
 * @access public
 */
function unbindValidation($type, $fields, $require=false)
{
    if ($type === 'remove')
    {
        $this->validate = array_diff_key($this->validate, array_flip($fields));
    }
    else
    if ($type === 'keep')
    {
        $this->validate = array_intersect_key($this->validate, array_flip($fields));
    }
    
    if ($require === true)
    {
        foreach ($this->validate as $field=>$rules)
        {
            if (is_array($rules))
            {
                $rule = key($rules);
                
                $this->validate[$field][$rule]['required'] = true;
            }
            else
            {
                $ruleName = (ctype_alpha($rules)) ? $rules : 'required';
                
                $this->validate[$field] = array($ruleName=>array('rule'=>$rules,'required'=>true));
            }
        }
    }
}


Usage in the controller

(The following example REMOVES everything from $this->User->validate EXCEPT 'nickname' and sets nickname to 'required'=>true)
$this->User->unbindValidation('keep', array('nickname'), true);

(The following example REMOVES 'agree_to_tos' from $this->User->validate and sets all remaining fields to 'required'=>true)
$this->User->unbindValidation('remove', array('agree_to_tos') ,true);