Odoo fields computed for too many records - odoo

Question

I have some data in a tree structure. One of the fields are computed (not stored) using data from the children.
In a form view, I show the computed field and the parent field.
Because of this, I end up reading many records from the model - and Odoo seems to compute the computed field for all of these records, even though the view only needs the computed field for one record.
I thought this was caused by the prefetch mechanism, but I tried to set prefetch_fields=False in the context, and that didn't help.
Any idea how I can avoid computing all the unnecessary values? (Storing the computed field is not an option).
A quick example to give an idea of the construction:
parent_id = fields.Many2one(...)
child_ids = fields.One2many(...) # Inverse parent relation
comp = fields.Integer(compute="_compute_comp")
#api.one
def _compute_comp(self):
sum = 0
for c in self.child_ids:
sum += c._get_complicated_value()
self.comp = sum
and a view with:
<field name="parent_id" />
<field name="comp" />
comp is always computed for the children's children. With <field name="parent_id" /> it is also computed for ALL the parent's children.

Answer 1

you can use #api.depends
#api.depends
This decorator will trigger the call to the decorated function if any of the fields specified in the decorator is altered by ORM or changed in the form:
#api.depends('name', 'an_other_field')
def afun(self):
pass
Note:
when you redefine depends you have to redefine all #api.depends, so it
loses some of his interest.
One of the great improvement of the new API is that the depends are automatically inserted into the form for you in a simple way. You do not have to worry about modifying views anymore.
#api.one
#api.depends('child_ids')
def _compute_comp(self):
sum = 0
for c in self.child_ids:
sum += c._get_complicated_value()
self.comp = sum