GOLEM/golem_activity_registration/views/golem_activity_views.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2017 Fabien Bourgeois <fabien@yaltik.com>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
-->

<odoo>
  <data>

    <!-- Form -->
    <record id="golem_activity_form_inherit_registration"
      model="ir.ui.view">
      <field name="name">Activity Registrations and Places</field>
      <field name="model">golem.activity</field>
      <field name="inherit_id" ref="golem_activity.golem_activity_form" />
      <field name="arch" type="xml">
        <group name="places" position="inside">
          <field name="places" />
        </group>
        <page name="session" position="after">
          <page string="Members">
            <group>
              <field name="places_remain" readonly="True" />
              <field name="activity_registration_ids"
                context="{'default_activity_id': active_id, 'season_show': 0, 'activity_show': 0}" />
            </group>
          </page>
        </page>
      </field>
    </record>

    <!-- Tree -->
    <record id="golem_activity_tree_inherit_registration" model="ir.ui.view">
      <field name="name">Activity Tree registrations additions</field>
      <field name="model">golem.activity</field>
      <field name="inherit_id" ref="golem_activity.golem_activity_tree" />
      <field name="arch" type="xml">
        <tree position="attributes">
          <attribute name="colors">red: places_remain == 0;orange: places_remain &lt;= 4;</attribute>
        </tree>
        <field name="date_start" position="after">
          <field name="places" invisible="True" />
          <field name="places_remain" string="Remain" />
        </field>
      </field>
    </record>

    <!-- Search -->
    <record id="golem_activity_search_inherit_registration" model="ir.ui.view">
      <field name="name">Activity Search registrations additions</field>
      <field name="model">golem.activity</field>
      <field name="inherit_id" ref="golem_activity.golem_activity_search" />
      <field name="arch" type="xml">
        <filter name="season_default" position="after">
          <filter name="full_activity" string="Full"
           domain="[('places_remain', '=', 0)]" />
        </filter>
      </field>
    </record>

  </data>
</odoo>