Hello,i'll describe problem in the detail.The main problem is that i can't save 'res_model' field in 'ir.attachment' table. I use odoo v12.0.
Budget model
```
class AccountBudget(models.Model):
_name = "account.budget"
attachment_ids = fields.One2many('ir.attachment', 'id', string='Attachments')
```
Budget view
```
<field name="attachment_ids" context="{'default_res_model': 'account.budget',
'default_file_type': 'document'}">
</field>
```
As you can see, i set context wit default res_model. But when i click save button it doesn't save res_model.
File type work greatly.
This behavior only with One2Many relation. If i set 'attachment_ids' Many2Many all works fine.
But with Many2Many field i have one layer, that displayed all files, i don't need that.
How can i save attachment for certain res_model?