Most of the time, we want a custom method to perform some actions on a recordset. For this, we should use @api.multi, and in that case, the self argument will be the recordset to work with. The method's logic will usually include a for loop iterating on it. This is surely the most frequently used decorator.
If no decorator is used on a model method, it will default to @api.multi behavior.
In some cases, the method is prepared to work with a single record (a singleton). Here we could use the @api.one decorator, but this is not advised because for Version 9.0 it was announced it would be deprecated and may be removed in the future.
Instead, we should use @api.multi and add to the method code a line with self.ensure_one() ...
