Hi,

Instead of 'default_res_id': 'hotel.getdates,get_first_record_id()', you should use Python code to dynamically retrieve the ID of the first record. Assuming you have a function somewhere called get_first_record_id() that returns the id of the first record, you should pass it like this:

<record id="open_hotel_get_dates_tree" model="ir.actions.act_window">
    <field name="name">Get Calendar Files</field>
<field name="type">ir.actions.act_window</field>
<field name="res_model">hotel.getdates</field>
    <field name="view_mode">form</field>
<field name="context">{'form_view_initial_mode': 'view', 'default_res_id': get_first_record_id()}</field>
</record>

Hope it helps