no element type exists with getCriteria and custom element type

Question

I am working on a plugin using the getCriteria function, but for every Element Type I put, I always get an error:

No element type exists by the type “Comerce_Group”.

$criteria = craft()->elements->getCriteria("Comerce_Group");
$criteria->number = $number;
return $criteria->first();

And here is the Comerce_Group code:

class Comerce_GroupModel extends BaseModel
{  
    protected function defineAttributes()
    {
        return array (
            'id' => AttributeType::Number,
            'number' => AttributeType::String,
            'itemTotal' => AttributeType::Number,
        );
    }    
}

Answer 1

As Stephen pointed out, you're getting that error because your Commerce_GroupModel class is a Model that extends BaseModel, not an Element Type, which is what ElementsService->getCriteria() is looking for.

Are you sure you actually need a custom element type here? Depending on what you're going for, Models might be enough.