account_invoice_calendar_event_eiru/calendar_event.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>
        <record id="view_calendar_event_search" model="ir.ui.view">
            <field name="model">calendar.event</field>
            <field name="inherit_id" ref="calendar.view_calendar_event_search" />
            <field name="arch" type="xml">
                <xpath expr="." position="inside">
                    <field name="account_invoice_id" />
                    <filter name="account_invoices" string="Facturas" domain="[('account_invoice_id', '!=', False)]" />
                </xpath>
            </field>
        </record>
        <record id="view_calendar_event_calendar" model="ir.ui.view">
            <field name="model">calendar.event</field>
            <field name="inherit_id" ref="calendar.view_calendar_event_calendar" />
            <field name="arch" type="xml">

                <xpath expr="." position="inside">
                    <field name="account_invoice_id" />
                    <!-- <field name="location" position="attributes">
                        <attribute name="invisible">1</attribute>
                    </field> -->
                </xpath>
            </field>
        </record>
        <record id="view_calendar_event_form" model="ir.ui.view">
            <field name="model">calendar.event</field>
            <field name="inherit_id" ref="calendar.view_calendar_event_form" />
            <field name="arch" type="xml">
                <page string="Misc" position="inside">
                    <label for="account_invoice_id" />
                    <field name="account_invoice_id" />
                </page>
            </field>
        </record>
        <record id="view_calendar_event_form_popup" model="ir.ui.view">
            <field name="model">calendar.event</field>
            <field name="inherit_id" ref="calendar.view_calendar_event_form_popup" />
            <field name="arch" type="xml">
                <xpath expr="//group" position="inside">
                    <group name="account_invoice_calendar_event">
                        <field name="account_invoice_id" />
                    </group>
                </xpath>
            </field>
        </record>
    </data>
</openerp>