I have a basic calendar view with a fiew fields.

In odoo9 and 10 there was attribute attendee= that I could assign field with the attendees, but how can I make it work Odoo12 as there is no such attribute?

for example, I want to add partner_id as an attendee.

<record id="calendar_view" model="ir.ui.view">
    <field name="name">calendar.view</field>
    <field name="model">custom.calends</field>
    <field name="arch" type="xml">
        <calendar date_start="start" date_stop="completion" mode="month" color="user_id" >
            <field name="name"/>
            <field name="user_id"/>
             <field name="partner_id"/>
        </calendar>
    </field>
</record>