How to declare a related field with different types of relationships?

Question

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

Deepa Venkatesh · Answer

True, If you establish a related relation for One2many field would be indeed nonsense...

O2M of state is nothing but list of Records, and you establish a related for it which will be a single field, so resultant value will keep overriding with latest records ie states' country.. which is utterly meaningless..

Techincally speaking, this must be a bug, guess some how Odoo guys have overlooked this....

Anup Kandalkar · Answer

Here as you mention state_id is one2many fields, and want to declare related fields, which is not possible, bcz state_id will store more than one records. so how to define which one country will relate given field.  :(

Olivier Dony (odo) · Answer

If `state_id` was a `one2many` you could keep exactly the same syntax and it would work. The behavior for `fields.related` when going though a *2many relationship is to take the first record found (depending on the order of the target model), and then to continue. As to whether this makes any sense, it very much depends on the use case. It makes a bit more sense for read-only access than for changes through the related fields.

Ben Bernard · Answer

type="one2many", because state_id is one2many and each state_id has one country_id.

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