Hi, and thanks, this works. Great!

However, I still don't understand why. The principle I understand, but how odoo decides what field to use in comparison.

E.g. this uses name field: [('tag_ids','=','TAGNAME')]

Whereas this uses id: ("tag_ids","in",[123])

I would understand in better if we would always use explicit field definition, like 'tag_ids.id', but here seems to be some heuristic I do not understand, and is not documented anywhere? Is it related to the operator ('=' vs. 'in'), or is it determined by value type or what?

One2many and Many2many fields like tag_ids in this case, return the recordset. When used in a comparison without a specific field, they reference the name field defined for the model. A good example of seeing this in action is in the Export functionality - if you export the field tag_ids you will get the name field but if you specifically select one of the fields the value of that field will get exported.

Thanks for the heuristic explanation, Paresh. But here ("tag_ids","in",[123]), Odoo is still using the recordest without any specific field, and is still correctly using the field "id" instead of the "name".