CakePHP Call to a member function save() on a non-object

Let's start with a simplified version my code:

Model: Sku.php

class Sku extends AppModel {

}

Controller: SkusController.php

class SkusController extends AppController {

    public function admin_add() {

        $this->layout = 'admin';

        if($this->request->is('post')) {
            if($this->Sku->save($this->request->data)) {
                // Do stuff
            }
            else // Do stuff
        }

    }

}

View: Skus > admin_add.ctp

<?php echo $this->Form->create('Sku', array('type'=>'file')); ?>
<?php echo $this->Form->input('Sku.item_no')); ?>
<?php echo $this->Form->input('Sku.size'); ?>
<?php echo $this->Form->input('Sku.color'); ?>
<button type="submit">Save SKU</button>
<?php echo $this->Form->end(); ?>

When I submit the form I get the error Call to a member function save() on a non-object. At the beginning of my controller file if I add the following everything works fine and a new row is inserted into the skus table.

public $uses = 'Sku';

If I have used all the proper naming conventions shouldn't I be able to omit the previous line? Furthermore, If I change all of the file and class names to Test following the same naming conventions it works without the $uses variable. This leads me to believe I have some sort of conflict elsewhere in my code. Any suggestions as to why this may be happening or where to look for a potential problem?

Thanks in advance!

Solution

Edit: Looks like the inflector cant turn the plural to singular: http://dogmatic69.com/inflector/Skus. So either you have to go with $uses or you add the rule to the inflector. See the inflector configuration.

You're not using an array or boolean for the Controller::$uses property.

public $uses = 'Sku';

Should be:

public $uses = array('Sku');

Actually you don't have to define it at all if the the controller and model match the conventions.

Read the documention http://api.cakephp.org/2.4/class-Controller.html#$uses

$uses An array containing the class names of models this controller uses.

Example: public $uses = array('Product', 'Post', 'Comment');

Can be set to several values to express different options:

true Use the default inflected model name.

array() Use only models defined in the parent class.

false Use no models at all, do not merge with parent class either.

array('Post', 'Comment') Use only the Post and Comment models. Models Will also be merged with the parent class.

The default value is true.