Hello,
You have multiple database in system? check odoo.conf for dbfilter parameter..

The thing is that the system is required to have multiple active DBs at the same time.

Can you elaborate more about this?

Hi,

Thanks for clarifying - this makes the problem much clearer.

You are right, the ?db=mydb parameter alone does not work for anonymous endpoints because Odoo's dispatcher rejects the request with a 404 before it even reads that parameter in a multi-DB setup. The DB selection needs to happen at the dispatcher level, earlier in the request lifecycle.

we have implemented this in a real project.
We built a custom Odoo module for a client who needed anonymous API access across a multi-DB Odoo instance - specifically for a mobile app integration where the calling system had no session context. The setup involved:

A custom ir.http override to intercept the DB name from a request header (X-Odoo-Database) before Odoo's dispatcher rejected the request
All custom endpoints decorated with auth='none' and routed outside the standard session-based flow
A lightweight token validation layer inside the endpoint itself (since there is no Odoo session, you handle your own auth logic)

It worked reliably in production on a 3-DB Odoo 16 instance.

Here is the approach that works for you:
Override _pre_dispatch in ir.http
In your custom module, extend ir.http and override the _pre_dispatch (or _get_default_session depending on your Odoo version) to read the database name from the request early - before routing resolves:

from odoo import models
from odoo.http import request, db_filter

class IrHttp(models.AbstractModel):
_inherit = 'ir.http'

@classmethod
def _pre_dispatch(cls, rule, args):
# Read ?db= param or X-Odoo-Database header early
db = (
request.httprequest.args.get('db')
or request.httprequest.headers.get('X-Odoo-Database')
)
if db and db in db_filter([db]):
request.session.db = db
return super()._pre_dispatch(rule, args)

--------------------------------------------------------------------------------------------------
Then your custom route should be decorated like this:

@http.route('/api/custom/do-something',
type='json',
auth='none', # critical
csrf=False,
save_session=False)
def do_something(self, **kwargs):
...
________________________________________________________________________________________________________
A few important notes:

- The auth='none' is mandatory - auth='public' will still try to resolve a user session which requires a DB context.
- Make sure your endpoint does not touch any ORM or recordset at the point of entry before the DB is set.
- If you are on Odoo 16+, the dispatcher was refactored - let us know your version and we can adjust the override accordingly.

This pattern has been implemented for similar anonymous API gateway scenarios and works reliably in multi-DB setups.
Hope this works for you! Feel free to reach out for further discussion.

Regards,
santosh.sekwadia@zehntech.com

Thanks a lot for the answer. I get the idea now. I'm using Odoo17 so the dispatcher behaves differently now.