many2manyattendeeexpandable

The attendee widget is designed for a form, where there is room for a row of avatars. In the calendar, the same information has to fit in a popover next to a small event block, and a company-wide meeting with forty invitees would fill it entirely.

This widget solves that by starting collapsed. Instead of every avatar it shows the numbers: how many people are invited, how many accepted, how many declined, and by subtraction how many have not answered. An expander opens the full attendee list underneath, with all the icons and flags the parent widget provides.

Nothing else changes. It is a direct subclass, so the status call, the icon map, the missing email flag, the availability flag and the organizer sort all behave exactly as they do on the full widget.

This is a small but instructive piece of interface design: the same data, two densities, chosen by where it appears. A count answers the question you have while scanning a calendar, which is whether the meeting is happening. The full list answers the question you have once you have decided to look, which is who exactly.

The pattern generalizes to any relation that is short on some records and long on others. Showing the summary first and making expansion cheap avoids designing for the worst case, which is what an always-expanded list forces you to do.

One thing to know operationally: the counts are read when the popover opens. If replies arrive while you are looking at it, the numbers will not move until you reopen it.

The core usage

<field name="partner_ids"
       widget="many2manyattendeeexpandable"
       write_model="calendar.filters" filters="1"/>

Used in the calendar side panel, where space is tight and the collapsed summary is the point.

The count fields it reads

<field name="attendees_count" invisible="1"/>
<field name="accepted_count" invisible="1"/>
<field name="declined_count" invisible="1"/>

All three are read by literal name in setup. Missing any of them makes the derived undecided count wrong rather than absent.

The full list instead

<field name="partner_ids" widget="many2manyattendee"/>

The parent widget, for a form where there is room to show every avatar.

The subclass is fifteen lines. It points at its own template, holds one piece of local state for whether the list is expanded, reads three counts in setup and computes a fourth, and exposes a toggle for the expander.

Reading the counts in setup rather than in getters is the decision worth recording. It makes the summary a snapshot of the moment the component was created, which for a calendar popover is exactly right, since the popover is short-lived and recreated each time it opens. On a long-lived form it would be a limitation.

The undecided count is not a field. It is the total minus the accepted and declined counts, computed once alongside them. That means it inherits any staleness in the three fields and, if a custom view supplies only some of them, it will silently come out wrong rather than missing.

Odoo 18 did one thing this version does not. It contained an effect that, on non-mobile screens, looked up the calendar popover in the document and repositioned it against the event block, so that expanding the attendee list did not push the popover off screen. Odoo 19 removed that entirely, presumably because the popover positioning is now handled generically.

The development branch keeps the same structure and moves the expander toggle out of the component, which is a template-level change rather than a behavioral one.

Odoo 20 is expected at Odoo Experience in Brussels, 24 to 26 September 2026. The development branch is unstable and this may still change; we re-verify the page after release.

No behavior change of its own. The counts, the derived undecided figure and the collapsed default are identical. The expander's toggle method is removed from the component, which means the template handles it directly, and the local state moves to the new reactive helper.

It does inherit the parent widget's Odoo 20 changes, which are more substantial: a new base, a dedicated attendee tag component and the new icon set. See the attendee widget's own page for those.