Help on entities

$allowedFields is really necessary? i don't got it very well because all attributes where in the entity and this makes me confused

No, you can set this in your models $protectFields = false;
But, I usually fill them out because regardless if you write entity fields or not, $allowedFields is the one that handles "filtering" of data. Basically if you do this: $product->fill($_POST) - you may get stuff you don't need in there and with $allowedFields it cross-references what is "valid" and what gets left out.

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Theres one example on entities I would like to see though.
How to handle business logic of a bunch of fields.
Currenty I do this: $product->fill($input) with $input variable holding an array of processed data I handled elsewhere in my controller.

I know I can do business logic in entities though, which would clean up my code somewhat, but I'm not sure how to go about this.
I want to actually do this: $product->fill($_POST)
And within entities I want to check each $_POST value - if it is '' set it to null, if it has a trailing space in the beginning or end i want to trim() (users tend to press the spacebar inadvertently). And for one of the $_POST fields - the url I want to do this: url_title($_POST['posted_url'])
Anyone got a good example on this?

You can see things I made with codeigniter here: itart.pro its not overly impressive as I have very little time to learn.