'Parameters
item_id: id of the item in the model
string or int
order_by_id: bool
If True order by user_id otherwise by the preference values.
default = True
Returns
Return all existing Preferences expressed for that item,
ordered by user id (if order_by_id is True) or by the preference values
(if order_by_id is False), as an array.'

def preferences_for_item(self, item_id, order_by_id=True):

    raise NotImplementedError('cannot    instantiate    Abstract    Base    Class')
