Let's see the classic example of a related field: you have an object city, which has a field state_id, and you need to show its country.
'country_id': fields.related(
'state_id',
'country_id',
type="many2one",
relation="res.country",
string="Country",
store=False)
The object city has a field state_id, which is a many2one, and the object state has a field country_id, which is also a many2one.
Now, what would happen if the type of the field state_id were one2many (and the type of country_id kept being many2one)? How should I declare the related field country_id?
This is obviously a nosense with those fields, but it's only an example to make easier to understand my question.
