Odoo domain_filter not working (always enforcing JOIN) - postgresql

Question

I am having a problem creating a filter on Odoo 11.0 Community Edition.
On my domain class I have a self-relationship with a column called parent_id. I am trying to make a search filter, but even if I add one condition to avoid make the join, it's still not working.
Here is my domain definition:
class Subscription(models.Model):
_name = "subscription"
_rec_name = 'name'
parent_id = fields.Many2one(
'subscription',
string="Derived From",
index=True,
readonly=True
)
code = fields.Char(
string="Reference",
required=True,
index=True,
readonly=True,
copy=False
)
# other field definitions ...
and here is the filter that I am trying to do:
<record id="search_view_subscription" model="ir.ui.view">
<field name="name">subscription.search</field>
<field name="model">subscription</field>
<field name="arch" type="xml">
<search string="Subscriptions">
<field name="code" string="Subscription"
filter_domain="[
'|',
'&',
('parent_id', '=', False),
('code', 'ilike', self),
'&',
('parent_id', '!=', False),
('parent_id.code', 'ilike', self)
]"
/>
<!-- ... other filters working -->
</search>
<field>
</record>
I am not sure if the prefix notation is correct to do what I want, but essentially what I am trying to do is to recover from the database all the records that match the condition:
code ilike '%CERTAIN_VALUE%' OR parent_id.code ilike '%CERTAIN_VALUE%'
Where CERTAIN_VALUE is the user input from the treeview screen.
It seems the condition ('parent_id', '=', False) is being ignored

Answer 1

The filter_domain attribute can contain an arbitrary domain, so you're restricted neither to searching for the same field you named in the name attribute nor to using only one term. The self variable is what the user filled in, and also the only variable that you can use here. Here's a more elaborate example from the default search view for partners:
<search >
<field name="name"
filter_domain="[ '|', '|',
('display_name', 'ilike', self),
('ref', '=', self),
('email', 'ilike', self)]"/>
</search>
pay attention
Works in search tags <search> </search>