Removing a belongsTo from a model shows warning Model 'x' is not associated with model 'y' - cakephp

Question

I am new to CakePHP and I am having to maintain/develop a CakePHP application and struggling with removing a BelongsTo in one of the models.
The code has been copied from another project that used a lot more related tables. In the new project I do not need the relationships because it is creating LEFT JOINS in the queries that I really want to get rid of in order to speed things up. So I went in to the model and removed the $belongsTo property..
When I go to the home page I now get a warniing:-
Warning (512): Model "Product" is not associated with model "ParentProduct"
[CORE/Cake/Model/Behavior/ContainableBehavior.php, line 343]
If I turn off debugging it is not shown but I would like to know why this message is being generated. I am unable to find any information on how I should go about removing the belongsTo relationships.
Any help appreciated.

Answer 1

So I went in to the model and removed the $belongsTo property
Because you're asking for it
This kind of error is displayed when using the containable behavior incorrectly.
E.g. Consider User hasMany Article, and the following code:
$User->find('all', array(
'contain' => array(
'Article'
)
));
This would return all users and their articles (only), irrespective of any other associations that exist.
If an association is requested that isn't defined:
$User->find('all', array(
'contain' => array(
'Article',
'Comment'
)
));
Containable will generate a warning so that you, the developer, can know that there will be no Comments in your results which either indicates a typo or another kind of development error (Ah... it's User<-Article<-Comment).
This is in-keeping with what you describe since the model associations have been modified but (evidently) not the application code.

Answer 2

The message is been generated (most probably) because in your controller (check the ParentProductsController first) is something like
$this->ParentProductsController->Product->find();
That association of models no longer exists because you wanted to get rid of it, so there's no way for ParentProducts to call Product. You need to change calls like that to
ClassRegistry::init('the_name_of_the_model');
(in this case ClassRegistry::init('Product');) or load the model with
$this->loadModel('Product');
Now, this only is necessary when you call models not related to the current controller. If you are calling Product->find from the ProductsController, there will be no error.
Ok, that's the cause of the error.
But now: I don't recommend you deleting the association. There's really no need and your removing a logical association in the code even though it's still there in the database. There are other ways to avoid left joins and useless queries to the database without cutting someone a limb.
If you want to speed things up, read about Containable Behavior, and set all models to $recursive = -1 (recursive doc). That way you won't get LEFT JOINS unless you explicitly say so.